Image coding apparatus, image coding method, image decoding apparatus and image decoding method

ABSTRACT

A coded bit stream generated on a coding side consists of a VO header, a VOL header, a GOV header, a VOP header and VOP data, and the VOL header multiplexes an object intra-coded indicator signal indicating whether all the VOP data contained in a VOL or GOV are intra coded or not. This enables a decoding side to recognize whether all the VOP data contained in the VOL or GOV in the coded bit stream are intra coded or not by only analyzing the object intra-coded indicator signal. This can facilitate such processings as frame skip control or random access of the VOPs.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of application Ser. No. 11/707,922,filed on Feb. 20, 2007, allowed on Oct. 23, 2007 now U.S. Pat. No.7,362,907, which is a Divisional of application Ser. No. 11/231,835filed on Sep. 22, 2005 now U.S. Pat. No. 7,197,188, which is adivisional of application Ser. No. 09/530,136 filed on Apr. 27, 2000,now U.S. Pat. No. 7,127,110, and for which priority is claimed under 35U.S.C. §120. Application Ser. No. 09/530,136 is the national phase ofPCT International Application No. PCT/JP98/04815 filed on Oct. 23, 1998under 35 U.S.C. §371, which claims priority of Application No. 9-293940filed in Japan on Oct. 27, 1997 and Application No. 10-054694 filed inJapan on Mar. 6, 1998 under 35 U.S.C. §119. The entire contents of eachof the above-identified applications are hereby incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image coding apparatus and an imagecoding method for generating a coded bit stream by coding images, and animage decoding apparatus and an image decoding method for receiving acoded bit stream and for decoding an image signal contained in the codedbit stream, and more particularly to an image coding apparatus and animage coding method according to MPEG-4 for coding images on an objectby object basis, and to an image decoding apparatus and an imagedecoding method according to MPEG-4 for decoding a coded bit streamgenerated by coding images on an object by object basis.

2. Background Art

Conventionally, as a method of coding or decoding an image signal,MPEG-4 (Moving Picture Experts Group Phase-4) is known which iscurrently in progress toward standardization by ISO/IEC JTC11/SC29/WG11,for example.

The MPEG-4 is a method that captures a moving picture sequence as acollection of moving image objects that take any shapes in time andspace, and carries out coding and decoding based on individual movingimage objects.

FIG. 1 shows a video data structure according to the MPEG-4 standard.

In the MPEG-4, a moving image object including a time axis is referredto as a Video Object (VO), components of the VO are each referred to asa Video Object Layer (VOL), components of the VOL are each called aGroup of Video Object Plane (GOV), and the image data that representsthe momentary state of the GOV and forms a unit of coding is called aVideo Object Plane (VOP). For example, the VO corresponds to individualtalkers and the background in a videoconference scene, the VOL is a unitof the talkers and the background with a particular temporal and spatialresolution, and the VOP is the momentary image data of the VOLs(corresponding to frames). The GOV is a data structure consisting of aplurality of VOPs, which is used as a unit of edition and random access,and not necessarily required in coding.

FIG. 2 shows a concrete example of the VOPs. FIG. 2 shows two VOPs,(VOP1 represents a man, and VOP2 represents a picture on a wall). EachVOP consists of texture data representing color gradation levels andgeometric data representing the shape of the VOP. The texture dataconsists of 8-bit luminance signal and color difference signals (with asize ½ sub-sampled in the horizontal and vertical directions withrespect to the luminance signal). The geometric data is binary matrixdata that assigns “1” to the inside of the VOP and “0” to the outsidethereof, and has the same image size as the luminance signal (althoughthe geometric data has 8-bit width per pixel, and the inside of the VOPis assigned “255” and the outside assigned “0” in practice, it isassumed in the following that they are assigned the binary value “1” and“0” for convenience sake).

In the moving picture representation based on the VOPs, a conventionalframe image is obtained by placing the plurality of VOPs in position ina picture. If the shape of the VOP is rectangular and time-invariant,the VOP becomes synonymous with the frame. In this case, the geometricdata is absent, and only the texture data is coded.

FIG. 3 shows an example of a conventional coded bit stream. A bit stringcalled a start code is placed at the initial positions of the VO, VOL,GOV and VOP headers and of the VOP data. The start code is a unique word(a bit string that can be interpreted uniquely) for indicating thebeginning of the individual header information and VOP data information.The individual header information contains information required fordecoding data in that and its lower layers, and information representinglayer attribute. For example, the VOL header information containsinformation required for decoding the VOPs constituting the VOL. The VOPdata consists of the image data divided into macroblocks, a unit blockto be coded. Although the VOP data as shown in FIG. 3 does not usuallyinclude the start code, the start code can be added to every set of aplurality of macroblocks. The VOP header information contains codingtype information as to whether the VOP is intra coded or inter coded.The intra coding refers to a coding mode that codes the VOP to be codedusing only information about the VOP itself without using theinformation associated with other VOPs. In contrast, the inter codingrefers to a coding mode that codes the information on the VOP using theinformation associated with previous and following VOPs.

With the foregoing structure, the conventional image coding apparatusand image decoding apparatus can identify the coding mode of the VOPdata only after it analyzes the coding type information contained in theVOP header information in the coded bit stream. As a result, althoughthe coding side codes the entire VOP data in such units as VOL, GOV orthe like of the object using only the intra coding, the decoding sidemust analyze the header information of the individual VOPs to identifythe coding mode applied to the VOPs.

Therefore, although the coding side codes the entire VOP data in theunits like VOL or GOV of the object using only the intra coding, toachieve instantaneous access to a VOP at a desired time, or to carry out“frame skip control” for decimating image signal to be coded inaccordance with the load of a decoder, the decoding side cannot identifythe desired VOP to be accessed or the VOP to be decoded in the frameskip control until it recognizes the predictive structure and timeinformation of the coded bit stream by analyzing the coded data of allthe VOPs. This presents a problem of making the decoding processingdifficult and prolonging the decoding.

SUMMARY OF THE INVENTION

The present invention is implemented to solve the foregoing problem.Therefore, it is an object of the present invention to provide an imagecoding apparatus, image coding method, image decoding apparatus andimage decoding method capable of enabling, when all the images containedin a moving picture sequence undergo only the intra coding, the imagedecoding apparatus to carry out access to the very image at a desiredtime, so as to facilitate smooth decoding processing like the frame skipcontrol, thereby shortening the decoding processing.

In particular, an object of the present invention is to provide an imagecoding apparatus, image coding method, image decoding apparatus andimage decoding method capable of enabling the image decoding apparatusto carry out access to the very image at a desired time, and tofacilitate smooth decoding processing like the frame skip control,thereby shortening the decoding processing, when the coding side codesall the VOPs contained in the units like VOL or GOV of the object usingonly the intra coding according to the MPEG-4 standard that decodes theimages consisting of a plurality of objects on an object by objectbasis.

The image coding apparatus or image coding method according to thepresent invention encodes images contained in a moving picture sequencein accordance with intra-coding instruction information instructingwhether all the images contained in the moving picture sequence are tobe intra coded or not; and multiplexes an encoded image coded signalwith intra-coded indicator information indicating whether all the imagescontained in the moving picture sequence are intra coded or not.

This enables the decoding side to decide as to whether all the imagedata contained in the moving picture sequence undergo the intra codingor not without decoding the headers or overheads of the individual imagedata constituting the moving picture sequence. This offers an advantageof being able to generate the coded bit stream that enables the decodingside to carry out decoding with simply varying display rate or decodingrate, and to make random access to the image at a desired time withease.

The image decoding apparatus or image decoding method according to thepresent invention analyzes, in a coded bit stream, intra-coded indicatorinformation indicating whether all images contained in a moving picturesequence are intra coded or not; and decodes the images contained in themoving picture sequence in accordance with the intra-coded indicatorinformation.

This enables the decoding side to decide as to whether all the imagedata contained in the moving picture sequence undergo the intra codingor not without decoding the headers or overheads of the individual imagedata constituting the moving picture sequence. This offers an advantageof being able to enable the decoding side to carry out decoding withsimply varying display rate or decoding rate, and to make random accessto the image at a desired time with ease.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a video data structure according to theMPEG-4;

FIG. 2 is a diagram showing a concrete example of VOPs;

FIG. 3 is a diagram showing an example of a conventional coded bitstream;

FIG. 4 is a block diagram showing an internal configuration of a VOPencoder in an embodiment 1 in accordance with the present invention;

FIG. 5 is a flowchart illustrating the operation of the VOP encoder ofFIG. 4;

FIG. 6 is a flowchart illustrating the operation of the INTRA/INTERdecision section 14;

FIG. 7 is a block diagram showing a configuration of the headermultiplexer 8 as shown in FIG. 4;

FIG. 8 is a diagram showing an example of a coded bit stream 30 outputfrom the VOP encoder of the embodiment 1 in accordance with the presentinvention;

FIG. 9 is a diagram showing an example of a coded bit stream 31 outputfrom the VOP encoder of the embodiment 1 in accordance with the presentinvention;

FIG. 10 is a block diagram showing a configuration of the headermultiplexer 8 of the embodiment 1 for generating the coded bit stream 31as shown in FIG. 9;

FIG. 11 is a block diagram showing a configuration of a VOP encoder inan embodiment 2 in accordance with the present invention;

FIG. 12 is a block diagram showing a configuration of the headermultiplexer 8 as shown in FIG. 11;

FIG. 13 is a diagram showing an example of a coded bit stream 37 outputfrom the VOP encoder of the embodiment 2 in accordance with the presentinvention;

FIG. 14 is a diagram showing an example of a coded bit stream 38 outputfrom the VOP encoder of the embodiment 2 in accordance with the presentinvention;

FIG. 15 is a diagram showing an example of a coded bit stream 39 outputfrom the VOP encoder of the embodiment 2 in accordance with the presentinvention;

FIG. 16 is a diagram showing an example of a coded bit stream 40 outputfrom the VOP encoder of the embodiment 2 in accordance with the presentinvention;

FIG. 17 is a diagram showing an example of a coded bit stream 41 outputfrom the VOP encoder of the embodiment 2 in accordance with the presentinvention;

FIG. 18 is a block diagram showing an internal configuration of a VOPdecoder in an embodiment 3 in accordance with the present invention;

FIG. 19 is a flowchart illustrating the operation of the image decodingapparatus as shown in FIG. 18;

FIG. 20 is a flowchart illustrating the operation of the INTRA/INTERdecision section 54 as shown in FIG. 18;

FIG. 21 is a block diagram showing the details of the internalconfiguration of the header analyzer 42 in the embodiment 3 as shown inFIG. 18;

FIG. 22 is a block diagram showing an internal configuration of theframe skip controller 69 as shown in FIG. 21;

FIG. 23 is a flowchart illustrating the operation of the header analyzer42 as shown in FIG. 21;

FIG. 24 is a flowchart illustrating the operation of the VOP headeranalyzer 62;

FIG. 25 is a diagram for illustrating modulo-time base 65 and VOP timeincrement 68;

FIG. 26 is a block diagram showing another internal configuration of theheader analyzer 42 of the embodiment 3 in accordance with the presentinvention;

FIG. 27 is a block diagram showing an example of the image decodingapparatus of the embodiment 3 in accordance with the present inventionapplied to a system for regenerating a single image by combining decodedimage signals of a plurality of objects;

FIG. 28 is a diagram showing a coded bit stream including VOP rateinformation in the VOL header;

FIG. 29 is a block diagram showing an internal configuration of theheader analyzer 42 of an embodiment 4 in accordance with the presentinvention;

FIG. 30 is a block diagram showing the frame skip VOP controller 86 ofthe embodiment 4 as shown in FIG. 29;

FIG. 31 is a flowchart illustrating the operation of the header analyzer42 of the embodiment 4 in accordance with the present invention;

FIG. 32 is a block diagram showing another configuration of the headeranalyzer 42 of the embodiment 4 in accordance with the presentinvention;

FIG. 33 is a block diagram showing an internal configuration of theheader analyzer 42 of an embodiment 5 in accordance with the presentinvention;

FIG. 34 is a block diagram showing the frame skip controller 98 of theembodiment 5 in accordance with the present invention;

FIG. 35 is a flowchart illustrating the operation of the header analyzer42 of the embodiment 5 in accordance with the present invention;

FIG. 36 is a flowchart illustrating the operation of the frame skipcontroller 98 of the embodiment 5 in accordance with the presentinvention;

FIG. 37 is a block diagram showing an internal configuration of theheader analyzer 42 of an embodiment 6 in accordance with the presentinvention;

FIG. 38 is a block diagram showing the decoded VOP selector 103 as shownin FIG. 37;

FIG. 39 is a flowchart illustrating the operation of the header analyzer42 of the embodiment 6 in accordance with the present invention;

FIG. 40 is a flowchart illustrating the detail processing of a VOPrandom access mechanism at step ST56 by the decoded VOP selector 103 ofthe embodiment 6 in accordance with the present invention;

FIG. 41 is a block diagram showing an internal configuration of theheader analyzer 42 of an embodiment 7 in accordance with the presentinvention;

FIG. 42 is a block diagram showing the decoded VOP selector 107 as shownin FIG. 41;

FIG. 43 is a flowchart illustrating the operation of the header analyzer42 of the embodiment 7 in accordance with the present invention; and

FIG. 44 is a flowchart illustrating the detail processing of a VOPrandom access mechanism at step ST66 by the decoded VOP selector 107 ofthe embodiment 7 in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The best mode for carrying out the invention will now be described withreference to the accompanying drawings to explain the present inventionin more detail.

Embodiment 1

In the embodiment 1 in accordance with the present invention, a VOPencoder will be described that employs the MPEG-4 video coding schemedisclosed in the ISO/IEC JTC1/SC29/WG11/N1796, and comprises a codingmeans and a multiplexing means. The coding means carries out codingbased on information as to whether only the intra coding is applied toall the VOPs contained in the unit such as a VOL or GOV of each objectwhich is an element of the present embodiment 1. The multiplexing meansadds to each object the information on whether only the intra coding isapplied to all the VOPs contained in the unit such as a VOL or GOV,thereby generating a coded bit stream. Here, the intra coding refers toa coding mode that codes the VOP to be coded using only the informationabout that VOP itself without using the information about remainingVOPs. Thus, intra-coded VOP can be decoded by itself.

Because the image coding apparatus of the present embodiment 1 is basedon the MPEG-4 video encoder that carries out coding on a VOP by VOPbasis, it is called a VOP encoder from now on. Since the operation ofthe existing VOP encoder is disclosed in the ISO/IECJTC1/SC29/WG11/N1796 and the like, the operation of the encoder itselfis only surveyed here, and the components of the present embodiment 1will be described in detail.

FIG. 4 shows a configuration of the VOP encoder of the presentembodiment 1. In FIG. 4, the reference numeral 1 designates a geometryencoder; 2 designates geometry coded data; 3 designates locally decodedgeometry data; 4 designates a motion-compensation predictor; 5designates motion information; 6 designates GOV multiplex information; 7designates an object intra-coding instruction signal; 8 designates aheader multiplexer; 9 designates a bit stream after header informationmultiplexing; 10 designates a video signal multiplexer; 11 designates apredicted image; 12 designates a subtracter; 13 designates a predictionerror image; 14 designates an INTRA/INTER decision section; 15designates texture data to be coded (referred to as an input image fromnow on); 16 designates macroblock-based coding mode information; 17designates a texture encoder; 18 designates texture coded data; 19designates a locally decoded prediction error image; 20 designates anadder; 21 designates locally decoded texture data; 22 designates amemory; 23 designates reference texture data; and 24 designates a codedbit stream.

Next, the operation of the VOP encoder of the present embodiment 1 asshown in FIG. 4 will be described briefly. FIG. 5 is a flowchartillustrating the operation of the VOP encoder of the present embodiment1 as shown in FIG. 4.

An input object image is supplied to the geometry encoder 1,motion-compensation predictor 4, INTRA/INTER decision section 14 andsubtracter 12. In this case, the geometric data of the input objectimage is supplied on every 16×16 pixel block basis called an alphablock, and the texture data of the input object image is also suppliedon every 16×16 pixel block basis called a macroblock.

First, the geometry encoder 1 encodes the input alpha block, and outputsthe geometry coded data 2 and locally decoded geometry data 3 (stepST1). Since the coding processing of the geometry encoder 1 is off thesubject of the present invention, the description thereof is omittedhere. The geometry coded data 2 is transferred to the video signalmultiplexer 10, and the locally decoded geometry data 3 is delivered tothe motion-compensation predictor 4 and texture encoder 17.

Subsequently, the motion-compensation predictor 4 reads the referencetexture data 23 from the memory 22, and carries out macroblock-basedblock matching to obtain the motion information 5 (step ST2).Specifically, the motion-compensation predictor 4 obtains the motioninformation 5 by carrying out the block matching of only an objectincluded in the macroblock on the basis of the locally decoded geometrydata 3. Then, the motion-compensation predictor 4 reads from the memory22 the reference tenure data 23 at the location corresponding to themotion information 5, and generates the predicted image 11 from thelocally decoded geometry data 3. The motion information 5 generated bythe motion-compensation predictor 4 is supplied to the video signalmultiplexer 10, and the predicted image 11 is fed to the subtracter 12and adder 20.

Then, the INTRA/INTER decision section 14 decides on the basis of theexternally set object intra-coding instruction signal 7 the coding modeof the individual macroblocks of the VOPs to be coded, and selects aninput image in response to the coding mode decided. The image selected(in the case of the inter coding, it is the prediction error image 13)is supplied to the texture encoder 17, and the macroblock-based codingmode information 16 decided is supplied to the video signal multiplexer10 (step ST3). Here, the object intra-coding instruction signal 7 isinformation indicating whether all the VOPs contained in the unit suchas a VOL or GOV are to be coded only by the intra coding or not, whichis set by a user operating a switch or inputting a command. When all theVOPs are to be coded by only the intra coding, the signal is turned ON(“1”), and otherwise it is turned OFF (“0”).

FIG. 6 is a flowchart illustrating the operation of the INTRA/INTERdecision section 14. The operation will now be described with referenceto FIG. 6. First, the operation is switched in response to the value ofthe object intra-coding instruction signal 7 (step ST3-1). When theobject intra-coding instruction signal 7 is ON, the INTRA/INTER decisionsection 14 selects the input object image as the input image 15, setsthe macroblock-based coding mode information 16 to the intra-codingmode, and supplies the input image 15 selected to the texture encoder 17(step ST3-2).

On the other hand, when the object intra-coding instruction signal 7input is OFF, the INTRA/INTER decision section 14 selects the codingmode for each macroblock according to the method defined by the ISO/IECJTC1/SC29/WG11/N1796, for example. Then, the INTRA/INTER decisionsection 14 selects as input image 15 the input object image when themacroblock-based coding mode selected is the intra-coding mode, but theprediction error image 13 when the macroblock-based coding mode selectedis the inter-coding mode, and supplies it to the texture encoder 17(step ST3-3). In addition, the INTRA/INTER decision section 14 suppliesthe video signal multiplexer 10 with the macroblock-based coding modeselected as the macroblock-based coding mode information 16.

Returning to the flowchart of FIG. 5, the texture encoder 17 encodes theinput image 15 according to the method defined by the ISO/IECJTC1/SC29/WG11/N1796, thereby obtaining the texture coded data 18 andlocally decoded prediction error image 19 (step ST4). In the course ofthis, the texture encoder 17 carries out the coding of only the objectin the block in response to the locally decoded geometry data 3. Thetexture encoder 17 transfers the texture coded data 18 to the videosignal multiplexer 10, and the locally decoded prediction error image 19to the adder 20.

The adder 20 sums up the predicted image 11 and the locally decodedprediction error image 19 to generate the locally decoded texture data21 (step ST5), and writes the sum to the memory 22 (step ST6). Theforegoing processings are iterated for each macroblock, and when theprocessings of the entire macroblocks included in a single VOP arecompleted, the coding processing of the single VOP is terminated.Otherwise, the coding processing of the remaining macroblocks iscontinued (step ST7).

The header multiplexer 8 multiplexes the individual items of the headerinformation into the bit stream 9, and supplies it to the video signalmultiplexer 10 (step ST8).

The video signal multiplexer 10 multiplexes the bit stream 9, whichconsists of the multiplexed items of the header information, with thegeometry coded data 2, motion information 5, texture coded data 18 andmacroblock-based coding mode information 16, and outputs the coded bitstream 24 (step ST9).

Next, the operation of the header multiplexer 8, which characterizes thepresent embodiment 1, will be described in detail.

FIG. 7 shows a configuration of the header multiplexer 8 as shown inFIG. 4. In FIG. 7, the reference numeral 25 designates a VO headermultiplexer; 26 designates a VOL header multiplexer; 27 designates a GOVheader multiplexer selector; 28 designates a GOV header multiplexer; and29 designates a VOP header multiplexer.

The VO header multiplexer 25 generates a bit stream into which the VOheader is multiplexed, and supplies it to the VOL header multiplexer 26.The VOL header multiplexer 26 multiplexes into the bit stream fed fromthe VO header multiplexer 25 various VOL header items including anobject intra-coded indicator signal 7′ as one of them. Here, the objectintra-coded indicator signal 7′ refers to the information on whether ornot all the VOPs contained in the unit such as a VOL or GOV are coded byonly the intra coding. The object intra-coded indicator signal 7′ can bemultiplexed as 1-bit information in the VOL header information, which isplaced at “1” when the object intra-coding instruction signal 7 is ON,and at “0” when it is OFF, for example. The bit stream after themultiplexing is supplied to the GOV header multiplexer selector 27.

The GOV header multiplexer selector 27 decides the output destination ofthe bit stream fed from the VOL header multiplexer 26 in accordance withthe GOV multiplex information 6 that indicates whether multiplexing ofthe GOV header is to be carried out or not. According to the MPEG-4, theGOV header need not be contained in the coded bit stream. Thus, theencoder of the present embodiment 1 can selectively multiplex the GOVheader using the GOV multiplex selector 27. It is obvious, however, theencoder can be configured such that it determines in advance as towhether the GOV header is to be multiplexed or not. In other words, theencoder can be configured such that it does not comprise the GOV headermultiplexer selector 27, and supplies the output of the VOL headermultiplexer 26 directly to the VOP header multiplexer 29 without passingthrough the GOV header multiplexer 28, or that it supplies the output ofthe VOL header multiplexer 26 to the VOP header multiplexer 29 throughthe GOV header multiplexer 28.

When the GOV multiplex information 6 indicates that the GOV header neednot be multiplexed, the bit stream is supplied to the VOP headermultiplexer 29 without passing through the GOV header multiplexer 28.

In contrast with this, when the GOV multiplex information 6 indicatesthat the GOV header must be multiplexed, the bit stream is supplied tothe GOV header multiplexer 28. In response to this, the GOV headermultiplexer 28 multiplexes the GOV header into the bit stream fed fromthe GOV header multiplexer selector 27, and supplies the output bitstream to the VOP header multiplexer 29.

Thus, the VOP header multiplexer 29 multiplexes the VOP header into thebit stream which is supplied directly from the GOV header multiplexerselector 27, or from the GOV header multiplexer selector 27 via the GOVheader multiplexer 28, and provides the output bit stream 9 to the videosignal multiplexer 10.

FIG. 8 shows an example of the coded bit stream 30 output from the VOPencoder of the present embodiment 1 in accordance with the presentinvention. It is an example of the coded bit stream 24 in FIG. 4. Thecoded bit stream 30, like the conventional coded bit stream as shown inFIG. 3, comprises a VO header 30 a, a VOL header 30 b, a GOV header 30c, a VOP header 30 d and VOP data 30 e, each of which consists of astart code and header information or data information. In the presentembodiment 1, the VOL header 30 b includes an object intra-codedindicator signal 7′ multiplexed thereinto. Thus, the object intra-codedindicator signal 7′ indicates that the entire VOP data 30 e constitutingthe VOP associated with the VOL header 30 b are intra coded.

Here, each VOP data 30 e includes texture data (not shown) and geometricdata (not shown) that are coded for each macroblock constituting a unitto be coded, and is multiplexed with the coding mode information 16 thatindicates as overhead information whether the macroblock is intra codedor inter coded for each macroblock. However, when the object intra-codedindicator signal 7′ is ON, that is, when the entire VOP data 30 e of theVOL or GOV are intra coded, it is unnecessary to multiplex the codingmode information 16 of each macroblock constituting the VOP data,thereby reducing the amount of information of the coded bit stream. Thisholds true in all the following embodiments.

Incidentally, the VOL header 30 b is set on the VOL (Video Object Layer)by VOL basis. Thus, when the VO consists of a plurality of VOL0 and VOL1as shown in FIG. 1, the VOL header 30 b is set for each VOL, and theobject intra-coding instruction signal 7 is also set for each VOL.

In addition, when the GOV header multiplexer selector 27 decides that itis unnecessary for the GOV header multiplexer 28 to multiplex the GOVheader, the coded bit stream 30 has a structure as shown in FIG. 8except the GOV header 30 c.

As described above, the present embodiment 1 has such a configurationthat multiplexes into the VOL header the object intra-coded indicatorsignal 7′ indicating that the entire VOP data, which constitutes the GOVsubordinate to the VOL or constitutes the VOL without using the conceptof the GOV, are intra coded. As a result, an image decoding apparatuscan decide as to whether all the VOPs contained in the object are intracoded or not by only decoding and analyzing the object intra-codedindicator signal 7′ without decoding the individual VOP headers. Thismakes it possible for the decoding apparatus side to carry out decodingwith varying the display rate or decoding rate with ease, and togenerate the coded bit stream that enables simple access to the VOPs ata desired time.

Although the object intra-coded indicator signal 7′ is multiplexed intothe VOL header 30 b in the coded bit stream 30 as shown in FIG. 8 in theforegoing description, this is not essential to the present invention.For example, the object intra-coded indicator signal 7′ can bemultiplexed into the GOV header 31 c in a coded bit stream 31 as shownin FIG. 9, so that the object intra-coded indicator signal is defined onthe GOV basis lower in rank than the VOL. This enables the coding andthe multiplexing of the object intra-coded indicator signal on the GOVbasis.

In this case, the header multiplexer 8 can be configured as shown inFIG. 10 in which the object intra-coded indicator signal 7′ is notmultiplexed by a VOL header multiplexer 32, but by a GOV headermultiplexer 33. Thus, the object intra-coded indicator signal 7′functions as the information indicating whether the entire VOP data 31 econtained in the GOV are intra coded or not, and is multiplexed togetherwith the GOV header information into the GOV header 31 c as shown inFIG. 9 by the GOV header multiplexer 33.

In addition, although the present embodiment 1 is configured such thatthe header multiplexer 8 generates the 1-bit object intra-codedindicator signal 7′ from the object intra-coding instruction signal 7,it is not essential to the present invention. For example, the objectintra-coded indicator signal 7′ can have more than one bit.Alternatively, when the object intra-coding instruction signal 7indicating whether the entire VOP data constituting the VOL or GOV areto be intra coded or not is represented in the form of bit information,the object intra-coding instruction signal 7 itself can be multiplexedas the object intra-coded indicator signal 7′.

Furthermore, although the coding apparatus of the present embodiment 1is implemented in the form of hardware as shown in FIG. 4 and so on,this is not essential to the present invention. For example, the codingapparatus can be implemented in software. In other words, the functionsof the present embodiment 1 can be implemented by means of a CPU or MPUthat executes the program as shown in FIGS. 5 and 6. This also appliesto all the following embodiments.

Embodiment 2

In the present embodiment 2 in accordance with the present invention, aVOP encoder will be described that comprises the following coding meansand multiplexing means in a video coding system according to the MPEG-4disclosed in the ISO/IEC JTC1/SC29/WG11/N1796. The coding means carriesout coding of all the VOPs contained in the unit such as a VOL or GOV inresponse to the object intra-coding instruction signal 7, theinformation indicating whether only intra coding is to be carried out ornot. The multiplexing means multiplexes into the coded bit stream theobject intra-coded indicator signal 7′ and display time multiplexidentification information 34. The object intra-coded indicator signal7′ is the information indicating whether all the VOPs contained in theunit such as a VOL or GOV undergo only the intra coding or not. Thedisplay time multiplex identification information 34 indicates whetherthe absolute display time information of all the VOPs contained in theunit such as a VOL or GOV is to be collectively multiplexed or not.

FIG. 11 shows a configuration of the VOP encoder in the presentembodiment 2. The VOP encoder as shown in FIG. 11 has a configurationvery close to the VOP encoder of the embodiment 1 as shown in FIG. 4.The basic operation of the encoder is also similar to that of theembodiment 1. The present embodiment 2 differs from the foregoingembodiment 1 in the structure of the header multiplexer 8. In FIG. 11,the reference numeral 34 designates the display time multiplexidentification information; and 35 designates a time code representingthe absolute display time of the individual VOPs. The remaining membersare identical to the corresponding members of FIG. 4 designated by thesame reference numerals. Here, only the header multiplexer 8 withdifferent structure from that of the embodiment 1 will be described.

FIG. 12 shows a configuration of the header multiplexer 8 as shown inFIG. 11. In FIG. 12, the reference numeral 36 designates a VOL headermultiplexer.

The header multiplexer 8 as shown in FIG. 11 carries out in its VOLheader multiplexer 36 the following multiplexing. Specifically, the VOLheader multiplexer 36 multiplexes the 1-bit object intra-coded indicatorsignal 7′ into the VOL header information; multiplexes the 1-bit displaytime multiplex identification information 34 into the VOL headerinformation when the object intra-coded indicator signal 7′ is ON, thatis, when it indicates that all the VOPs contained in the unit such as aVOL or GOV are intra coded; and multiplexes into the VOL headerinformation collectively the time code 35 indicating the absolutedisplay time of all the VOPs constituting the VOL in accordance with thedisplay time multiplex identification information 34.

Here, the time code 35 is time information disclosed in the IEC standardpublication 461 for “time and control codes for video tape recorders”.It is the information for defining in hours, minutes and seconds thedisplay time of the images (such as frames in MPEG-2 and VOPs in MPEG-4)constituting a moving picture. This offers an advantage of being able toaccess a desired frame only by designating the value of the time code 35by adding this information to each frame when carrying out frame basededition in a video editor for business use.

Since the remaining configuration is the same as the header multiplexer8 as shown in FIG. 7, only the operation of the VOL header multiplexer36 in FIG. 12 different from that of the embodiment 1 will be described.

The VOL header multiplexer 36 multiplexes information required into thebit stream supplied from the VO header multiplexer 25 in accordance withthe following rules 1)-5).

1) Multiplexing various VOL header information such as data needed fordecoding and decompressing the individual VOPs.

2) Multiplexing the object intra-coded indicator signal 7′.

3) Multiplexing the display time multiplex identification information 34when the object intra-coded indicator signal 7′ is ON, that is, when itindicates that all the VOPs contained in the unit such as a VOL or GOVare subjected to the intra coding only.

The display time multiplex identification information 34 is 1-bitinformation indicating whether to multiplex the time codes 35 in all theVOPs in the VOL into the VOL header information area. When the timecodes 35 in all the VOPs in the VOL are to be multiplexed into the VOLheader information, it is set to “1” representing ON, arid otherwise itis set at “0” representing OFF. When the object intra-coded indicatorsignal 7′ represents OFF, the display time multiplex identificationinformation 34 is not multiplexed.

4) Multiplexing, when both the object intra-coded indicator signal 7′and the display time multiplex identification information 34 are ON, thetime codes 35 in all the VOPs in the VOL into the VOL header informationsection as shown in FIG. 15 which will be described later. For example,when a certain VOL includes 30 pieces of the VOPs, 30 time codes 35 aremultiplexed into the VOL header information section.

5) Supplying the GOV header multiplexer selector 27 with the bit streampassing through the foregoing multiplexing processings.

FIGS. 13, 14 and 15 each illustrate a coded bit stream output from theVOP encoder of the present embodiment 2.

The coded bit stream 37 as shown in FIG. 13 illustrates a case when theobject intra-coded indicator signal 7′ is OFF, in which neither thedisplay time multiplex identification information 34 nor the time code35 is multiplexed into the VOL header information 37 b. In this case,relative time information, which indicates the relative time from thereference time code 35, that is, from the absolute display time that ismultiplexed into the GOV header 37 c to the time the VOP is displayed,is multiplexed into the VOP header information 37 d of the individualVOPs (the relative time information is either modulo-time based or VOPtime incremented, though not shown here). The decoding side decides thedisplay time of the VOPs according to the relative time information.

The coded bit stream 38 as illustrated in FIG. 14 represents the casewhen the object intra-coded indicator signal 7′ is ON, but the displaytime multiplex identification information 34 is OFF, in which case thetime code 35 is not multiplexed into the VOL header information 38 b. Asin FIG. 13, the relative time information is multiplexed into the VOPheader information 38 d of the individual VOPs. It indicates therelative time from the reference time code 35 or the absolute displaytime that is multiplexed into the GOV header 38 c to the time the VOP isdisplayed.

The coded bit stream 39 as illustrated in FIG. 15 represents the case inwhich both the object intra-coded indicator signal 7′ and the displaytime multiplex identification information 34 are ON. In this case, thetime codes 35 in all the VOPs in the VOL are multiplexed into the headerinformation section 39 b. In this case, the relative time information inthe VOP header information section 39 d can be multiplexed withoutchange, or multiplexing of the relative time information into the VOPheader information can be skipped to avoid the duplication with the timecodes in the VOL header information 39 b.

As described above, the present embodiment 2 is configured such that itmultiplexes into the VOL header the object intra-coded indicator signal7′ which indicates that all the VOP data constituting the VOL undergothe intra coding, the display time multiplex identification information34, and the time codes indicating the absolute display time of all theVOPs in the VOL. This makes it possible for the image decoding apparatusthat decodes the VOPs by receiving the bit stream generated by thepresent coding apparatus to decide as to whether all the VOPs containedin the VOL are intra coded or not, and whether the time codes of all theVOPs are collectively multiplexed or not, without decoding and analyzingthe individual VOP headers. This makes it possible for the decodingapparatus to readily identify the VOP to be decoded before startingdecoding of the VOP, and to carry out decoding with varying the displayrate and decoding rate, and to access the VOP at a desired time withease.

Although the foregoing example multiplexes into the VOL header theobject intra-coded indicator signal 7′, display time multiplexidentification information 34 and time codes 35 as in the coded bitstreams 37-39 illustrated in FIGS. 13, 14 and 15, this is not essentialto the present invention. For example, the coded bit stream can beconfigured as in the following examples 1 and 2.

EXAMPLE 1

As shown in the coded bit stream 40 of FIG. 16, the object intra-codedindicator signal 7′ can be multiplexed into the VOL header 40 b, whereasthe display time multiplex identification information 34 can bemultiplexed into the GOV header 40 c when the object intra-codedindicator signal 7′ of the VOL belonging to this GOV is ON, and the timecodes 35 of all the VOPs contained in the GOV layer can also bemultiplexed into the GOV header 40 c when the display time multiplexidentification information 34 is ON. In this case, the display timemultiplex identification information 34 indicates whether the time codes35 of all the VOPs contained in the GOV are multiplexed collectivelyinto the GOV header or not.

EXAMPLE 2

As shown in the coded bit stream 41 of FIG. 17, all the objectintra-coded indicator signal 7′, the display time multiplexidentification information 34 and the time codes 35 can be multiplexedinto the GOV header 41 c. In this case, the object intra-coded indicatorsignal 7′ indicates whether all the VOPs contained in the GOV are intracoded or not, and the display time multiplex identification information34 indicates whether the time codes 35 of all the VOPs contained in theGOV are multiplexed collectively into the GOV header or not.

Thus generating the coded bit stream makes it possible for the decodingside to readily identify the VOP to be decoded on the GOV basis, tocarry out decoding with varying the display rate and/or decoding rate,and to make simple access to the VOP at a desired time.

Embodiment 3

In the embodiment 3 in accordance with the present invention, a VOPdecoder will be described for regenerating VOP images by decoding thecoded bit stream generated by the VOP encoder described in the foregoingembodiment 1. More specifically, an image decoding apparatus will bedescribed for decoding the object intra-coded indicator signal 7′described in the foregoing embodiment 1 from the coded bit stream, andfor controlling the display of the decoded VOPS in accordance with thevalue of the signal 7′.

First, a configuration and operation of the image decoding apparatus(VOP decoder) in the present embodiment 3 will be described. Because theoperation of the existing VOP decoder is disclosed in the ISO/IECJTC1/SC29/WG11/N1796 and so forth, the operation of the VOP decoderitself will be only outlined here. In the following description, thefunction characterizing the VOP decoder of the present embodiment 3,that is, the function to decode the object intra-coded indicator signal,and to selectively decode the VOP images based on the value of thesignal will be mainly described. In the following description, it isassumed that the coded bit stream 30 as shown in FIG. 8 is input to theVOP decoder.

FIG. 18 shows an internal configuration of the VOP decoder of theembodiment 3 in accordance with the present invention 3. It is assumedhere that the VOP data consists of the texture data and geometric dataas in the embodiment 1, and that the decoder has the function to decodethese data from their compression data received.

In FIG. 18, the reference numeral 42 designates a header analyzer; 43designates a bit stream whose header information has been analyzed; 44designates a video signal analyzer; 45 designates geometry coded data;46 designates a geometry decoder; 47 designates decoded geometric data;48 designates texture coded data; 49 designates a texture decoder; 50designates decoded texture data; 51 designates motion information; 52designates a motion compensator; 53 designates decoded predictiontexture data; 54 designates an INTRA/INTER decision section; 55designates output texture data; 56 designates a memory; and 57designates reference texture data.

FIG. 19 is a flowchart illustrating the operation of the image decodingapparatus as shown in FIG. 18. The operation will now be described withreference to FIGS. 18 and 19.

First, the coded bit stream 30 is supplied to the header analyzer 42,which analyzes the VO header, VOL header, GOV header and VOP header inaccordance with prescribed syntax as will be described later (stepST10).

In the course of this, the object intra-coded indicator signal 7′multiplexed into the VOL header 30 b is also analyzed, and is suppliedto the INTRA/INTER decision section 54.

Subsequently, the bit stream 43, the header information of which isanalyzed by the header analyzer 42, is supplied to the video signalanalyzer 44. The video signal analyzer 44 analyzes the VOP data, dividesthe data into the geometry coded data 45, texture coded data 48 andmotion information 51, and supplies their to the geometry decoder 46,texture decoder 49 and motion compensator 52, respectively (step ST11).

The geometry decoder 46 decodes the geometry coded data 45 supplied, andoutputs the decoded geometric data 47 (step ST12).

The motion compensator 52 produces the decoded prediction texture data53 on the basis of the reference texture data 57 read from the memory 56and the motion information 51 supplied from the video signal analyzer 44(step ST13).

The texture decoder 49 restores the image data from the texture codeddata 48 in accordance with the prescribed scheme defined in the MPEG-4such as ISO/IEC JTC1/SC29/WG11/N1796, and generates the decoded texturedata 50 (step ST14). The decoded texture data 50 is supplied to theINTRA/INTER decision section 54.

The INTRA/INTER decision section 54 first makes a decision of the finaloutput texture data 55 in accordance with the object intra-codedindicator signal 7′ (step ST15).

FIG. 20 is a flowchart illustrating the INTRA/INTER decision operationat step ST15 by the INTRA/INTER decision section 54 in the presentembodiment 3.

First, in response to the value of the object intra-coded indicatorsignal 71′, the operation mode is switched (step ST15-1).

When the object intra-coded indicator signal 7′ is ON (“YES” at stepST15-1), the INTRA/INTER decision section 54 immediately outputs thetexture data 50 as the texture data 55 (step ST15-2).

In contrast with this, when the object intra-coded indicator signal 7′is OFF (“NO” at step ST15-1), the INTRA/INTER decision section 54selects its processing in response to the macroblock-based coding modeinformation 16 decoded by the video signal analyzer 44 (step ST15-3).Specifically, when the macroblock-based coding mode is the intra-codingmode (“YES” at step ST15-3), the INTRA/INTER decision section 54 outputsthe decoded texture data 50 as texture data 55 (step ST15-2), and whenit is the inter-coding mode (“NO” at step ST15-3), the INTRA/INTERdecision section 54 sums up the decoded prediction texture data 53 fedfrom the motion compensator 52 and the decoded texture data 50, andoutputs the sum data as the output texture data 55 (step ST15-4).

Returning to the flowchart of FIG. 19, because the output texture data55 is used in the subsequent VOP decoding, it is written into the memory56 (step ST16). The foregoing processing is carried out on themacroblock basis, which defines the coded (decoded) region predeterminedin the coding side and decoding side. In response to the detection ofthe start code of the next VOP, the decoding of the current VOP iscompleted, and if the start code of the next VOP is not detected, theprocessing returns to step ST11 to carry out the video signal analysisand onward, thus continuing the decoding of the macroblocks associatedwith the current VOP (step ST17).

To achieve this, the VOP decoder of the present embodiment 3 operates asfollows. First it decides as to whether the object intra-coded indicatorsignal 7′ is ON or not as illustrated in the INTRA/INTER processing ofFIG. 20. When the object intra-coded indicator signal 7′ is ON, that is,when all the VOP data 30 e constituting the VOL are intra coded, the VOPdecoder outputs the decoded texture data 50 as the output texture data55 without making the decision at step ST15-3 as to whether the codingmode is the intra-coding mode or not on the macroblock basis. This makesit possible to reduce the INTRA/INTER processing by the amount neededfor the processing of step ST15-3.

FIG. 21 shows an internal configuration of the header analyzer 42 of thepresent embodiment 3 as shown in FIG. 18, and particularly aconfiguration of the VOP header analyzer 55 in detail. In FIG. 21, thereference numeral 58 designates a start code analyzer; 59 designates aVO header analyzer; 60 designates a VOL header analyzer; 61 designates aGOV header analyzer; 62 designates a VOP header analyzer; 63 designatesa time code; 64 designates a modulo-time base analyzer; 65 designates amodulo-time base; 66 designates a decoded VOP absolute display timegenerator; 67 designates a VOP time increment analyzer; 68 designates aVOP time increment; 69 designates a frame skip controller; 70 designatesdecoded VOP absolute display time; 71 designates VOP rate information asthe display rate information set on the decoder side; and 72 designatesa video information header analyzer.

FIG. 22 is a block diagram showing an internal configuration of theframe skip controller 69 as shown in FIG. 21. In FIG. 22, the referencenumeral 73 designates an object intra-coded decision section; and 74designates a frame skip VOP decision section.

Next, the operation of the header analyzer 42 will be described indetail.

FIG. 23 is a flowchart illustrating the operation of the header analyzer42 as shown in FIG. 21, which illustrates the header analysis at stepST10 as shown in FIG. 19 in more detail.

The header analyzer 42 of the present embodiment 3 decodes the objectintra-coded indicator signal 7′ from the bit stream, and carries out theframe skip control based on the information provided by the signal.

Here, “frame skip control” refers to the following operation. Whencarrying out the image decoding using a software decoder in such anenvironment as only limited resources are available like a CPU andmemory in a PC (personal computer) and WS (workstation), and hence allthe coded VOPs cannot be decoded, the “frame skip control” restricts theVOPs to be decoded by skipping reading of the remaining VOPs. A methodof using the object intra-coded indicator signal 7′ will be describedlater.

In the header analysis by the header analyzer 42, the start codeanalyzer 58 first analyzes the start code contained in the coded bitstream 30 supplied (step ST18). The start code analyzer 58 supplies thebit stream to the VO header analyzer 59 when the analyzed start codeindicates a VO (step ST19), to the VOL header analyzer 60 when theanalyzed start code indicates a VOL (step ST20), to the GOV headeranalyzer 61 when the analyzed start code indicates a GOV (step ST21),and to the VOP header analyzer 62 when the analyzed start code indicatesa VOP (step ST22). Incidentally, the bit stream is supplied to the videosignal analyzer 44 when the VOP header analyzer 62 completes itsanalysis.

The VO header analyzer 59 analyzes the VO header information in the bitstream fed from the start code analyzer 58, and supplies the bit streamafter the analysis to the start code analyzer 58 (step ST23).

The VOL header analyzer 60 analyzes the VOL header information and theobject intra-coding indicator signal 7′ in the bit stream fed from thestart code analyzer 58, and supplies the bit stream after the analysisto the start code analyzer 58, and the object intra-coded indicatorsignal 7′ analyzed to the VOP header analyzer 62 and INTRA/INTERdecision section 54 (step ST24).

The GOV header analyzer 61 analyzes the GOV header information in thebit stream fed from the start code analyzer 58, and supplies the bitstream after the analysis to the start code analyzer 58 (step ST25). Inthe course of this, the time code 63 contained in the analyzed GOVheader information is supplied to the VOP header analyzer 62. Thedefinition of the time code 63 was given in the description of theembodiment 2.

Next, the operation of the VOP header analyzer 62 which corresponds tostep ST26 will be described.

FIG. 24 is a flowchart illustrating the operation of the VOP headeranalyzer 62.

First, the bit stream input to the VOP header analyzer 62 is supplied tothe modulo-time base analyzer 64, which analyzes the modulo-time base(step ST26-1), and supplies the modulo-time base 65 analyzed to thedecoded VOP absolute display time generator 66, and the bit stream afterthe analysis to the VOP time increment analyzer 67.

The VOP time increment analyzer 67 analyzes the VOP time increment inthe bit stream supplied (step ST26-2), and supplies the VOP timeincrement 68 analyzed to the decoded VOP absolute display time generator66, and the bit stream after the analysis to the frame skip controller69.

The decoded VOP absolute display time generator 66 generates the decodedVOP absolute time 70 from the modulo-time base 65, VOP time increment 68and time code 63, and supplies it to the frame skip controller 69 (stepST26-3).

Here, the modulo-time base 65 is the information indicating the time inseconds at which the VOP is to be displayed from a particular referencetime defined by the time code 63 as shown in FIG. 25. The amount ofseconds is represented by the number of “is” with the additional “0”indicating the end of the data.

The VOP time increment 68 is the information for fine adjusting thedisplay time with an accuracy of 1/1000 second within one second fromthe time determined by the modulo-time base 65 as shown in FIG. 25.Thus, the MPEG-4 can determine the VOP display time at an accuracy of1/1000 second. For example, the decoded VOP absolute display time (timecode) is generated as follows. When the modulo-time base 65 of the VOPto be decoded is “10”, the VOP time increment 68 is “000000” (when theVOP time increment is 6-bit accurate), and the reference time defined bythe time code 63 is “00 hour 12 minutes 34 seconds”, the absolutedisplay time of the decoded VOP becomes “00 hour 12 minutes 35 seconds”.

Subsequently, in the frame skip controller 69 as shown in FIG. 22, theobject intra-coded decision section 73 first determines the destinationof the input bit stream in accordance with the object intra-codedindicator signal 7′ (step ST26-4). More specifically, it decides as towhether the object intra-coded indicator signal 7′ is ON or not, andwhen it is ON, that is, when a decision is made that all the VOPs in theVOL are intra coded (“YES” at step ST26-4), the destination of the inputbit stream is switched to the frame skip VOP decision section 74. Incontrast, when the object intra-coded indicator signal is OFF (“NO” atstep ST26-4), the input bit stream is directed to the video informationheader analyzer 72.

The frame skip VOP decision section 74 makes a decision as to whetherthe VOP to be analyzed is the VOP to be decoded or not in response tothe decoded VOP absolute display time 70 fed from the decoded VOPabsolute display time generator 66, and to the VOP rate information 71that is set on the decoder side at a value lower than that of theencoder side for frame skipping (step ST26-5). When the frame skip VOPdecision section 74 decides that the decoding is necessary (“YES” atstep ST26-5), it supplies the input bit stream fed from the objectintra-coded decision section 73 to the video information header analyzer72. On the contrary, when it decides that the analysis is unnecessary(“NO” at step ST26-5), it supplies the bit stream to the start codeanalyzer 58.

Here, the VOP rate information refers to display rate informationindicative of the number of VOPs to be displayed per second, which VOPsare included in the prescribed unit such as the VOL and GOV. Forexample, when the VOP rate information is 2 pieces/second, two VOPs aredisplayed per second, which is equivalent to display each VOP for ½second. Accordingly, when the decoded VOP absolute time 65 of the firstVOP is “00 hour 01 minute 00 second” and the VOP rate information is 1piece/second, a decision is made that such VOPs are to be decoded thathave the absolute display time “00 hour 01 minute 01 second”, “00 hour01 minute 02 second”, and so on, which are obtained by successivelyadding one second to “00 hour 01 minute 00 second”. Thus, the decodingside can implement the VOP frame skipping by varying the VOP rateinformation 71 set on the decoder side and the VOP rate information seton the encoder side from 10 pieces/second to 2 pieces/second, forexample.

When the object intra-coded decision section 73 decides that the objectintra-coded indicator signal 7′ is OFF (“NO” at step ST26-4), or when itdecides that the object intra-coded indicator signal 7′ is ON (“YES” atstep ST26-4) and the frame skip VOP decision section 74 decides that theVOP to be analyzed has to be decoded (“YES” at step ST26-5), the videoinformation header analyzer 72 analyzes the video information headers inthe bit stream fed from the frame skip controller 69, and then suppliesthe bit stream to the start code analyzer 58 (step ST26-6). Thus, thestart code analyzer 58 supplies the video signal analyzer 44 with thecoded bit stream 43 whose headers are analyzed.

As a result, when the object intra-coded decision section 73 decides atstep ST26-4 that the object intra-coded indicator signal 7′ is OFF, itsupplies the bit stream fed to the VOP header analyzer 62 to the videoinformation header analyzer 72 without passing through the frame skipVOP decision section 74, thereby preventing the VOP frame skipping.

This is because it is not ensured in this case that all the VOPs in theVOL are intra coded, and hence all the VOPs must be analyzed over toobtain correct decoded images, because it is probable that thepredictive coding is carried out between the VOPs.

On the other hand, when the object intra-coded decision section 73decides at step ST26-4 that the object intra-coded indicator signal 7′is ON, the frame skip VOP decision section 74 decides at the next stepST26-5 as to whether the current VOP to be analyzed has to be decoded ornot in response to the VOP rate information 62 and the like, andsupplies the video information header analyzer 72 with only the inputbit stream with which a decision is made that the VOP decoding isrequired, thus enabling the VOP frame skipping.

This is because when the object intra-coded indicator signal 7′ is ON,it is ensured that all the VOPs in the VOL are intra coded, and hencethe decoder can immediately select a desired VOP to be decoded. Thismakes it possible to carry out the frame skip control freely.

As described above, the present embodiment 3 is configured such that itanalyzes, when decoding the coded bit stream including the objectintra-coded indicator signal 7′ multiplexed into the VOL header, theobject intra-coded indicator signal 7′. This makes it possible for thedecoder side to carry out, when the object intra-coded indicator signal7′ is ON, frame skipping of any VOPs in accordance with the VOP rateinformation 71 set on the decoder side so that the VOPs selected aresubjected to a processing such as display.

Although the foregoing description is made by way of example thatemploys the coded bit stream 30 as shown in FIG. 8 as a coded bitstream, in which the VOL is used as a unit, and the object intra-codedindicator signal 7′ is multiplexed into the VOL header 30 b, the presentinvention is not limited to this. For example, the coded bit stream 31as shown in FIG. 9 can be decoded in which the object intra-codedindicator signal 7′ is multiplexed into the GOV header 31 c. To achievethis, the header analyzer 42 can be configured as shown in FIG. 26 sothat not the VOL header analyzer 75 but the GOV header analyzer 76analyzes and decodes the object intra-coded indicator signal 7′multiplexed into the GOV header 31 c. This enables the frame skippingdisplay control on the GOV basis.

Furthermore, a system as shown in FIG. 27 can be configured. Itcomprises in correspondence with objects 77 a-77 c a plurality of VOPdecoders 78 a-78 c, each of which consists of the decoding apparatus ofthe present embodiment 3, and a composition section 79 that combines thedecoded image signals of the plurality of objects 77 a-77 c toreconstruct a single image 80. The system can perform such displaycontrol as reducing the display rate of a particular object by the VOPdecoders 78 a-78 c. This enables such control as reducing the displayrate in the ascending order of importance, when a plurality of objectswith the order of importance are combined into a picture.

Moreover, although it is assumed that the VOP decoder of the presentembodiment 3 is capable of decoding the coded bit stream generated bythe VOP encoder of foregoing embodiment 1, and receives and decodes thecoded VOP bit stream 30 or 31 as illustrated in FIG. 8 or 9, this is notessential to the present invention. For example, the present inventioncan include not only the system that receives the bit stream directlyfrom a coding apparatus and decodes it, but also a system that decodes acoded bit stream that is once encoded by the coding apparatus and thenstored in a recording medium like DVD. This also applies to the decodingapparatus of the other embodiments.

Embodiment 4

The present embodiment 4 in accordance with the present inventionrelates to another example of the VOP decoder described in the foregoingembodiment 3. Specifically, the VOP decoder of the present embodiment 4has a function to decode the bit stream including VOP rate informationmultiplexed into the VOL header together with the VOL header informationon the encoder side, and to carry out the display control based on thedecoded result.

Because the VOP decoder of the present embodiment 4 differs from the VOPdecoder of the embodiment 3 only in the structure of the header analyzer42, only this component will be described.

FIG. 28 shows an example of a coded bit stream 81 decoded by the VOPdecoder of the present embodiment 4. The coded bit stream 81 as shown inFIG. 28 corresponds to a bit stream including VOP rate information 87multiplexed into the VOL header 30 b of the coded bit stream 30 as shownin FIG. 8, which is set on the encoder side. Thus, the VOP rateinformation 87 is multiplexed into a VOL header 81 b in FIG. 28. The VOPrate information is such information as 30 VOPs/second when the encoderside encodes 30 VOPs per second, for example.

FIG. 29 is a block diagram showing an internal configuration of theheader analyzer 42 characterizing the present embodiment 4. In FIG. 29,the reference numeral 83 designates a start code analyzer; 84 designatesa VOL header analyzer; 85 designates a count obtained by counting thenumber of analyzed VOPs with which the start code is analyzed; 86designates a frame skip VOP controller; 87 designates VOP rateinformation set by the encoder; 88 designates decoded VOP selector; 89designates VOP select information; and 90 designates a VOP headeranalyzer.

FIG. 30 shows a configuration of the frame skip VOP controller 86 of thepresent embodiment 4 as shown in FIG. 29. In FIG. 30, the referencenumeral 73 designates an object intra-coded decision section; and 91designates a frame skip VOP decision section.

Next, the operation of the header analyzer 42 of the present embodiment4 will be described.

FIG. 31 is a flowchart illustrating the operation of the header analyzer42 of the present embodiment 4.

First, in the header analyzer 42 of the present embodiment 4, the startcode analyzer 83 analyzes the start code contained in the input codedbit stream 81 (step ST27). As a result, the start code analyzer 83supplies the bit stream to the VO header analyzer 59 when the analyzedstart code indicates the VO (step ST28), to the VOL header analyzer 84when the analyzed start code indicates the VOL (step ST29), to the GOVheader analyzer 61 when the analyzed start code indicates the GOV (stepST30), and to the frame skip VOP controller 86 when the analyzed startcode indicates the VOP, in which case, every time the start codeanalyzer 83 detects the VOP start code, it increments its counter andsupplies its count 85 to the frame skip VOP controller 86 (step ST31).Here, the count 85 is reset every time the VOL start code is detected.

The VO header analyzer 59 analyzes the VO header information in theinput bit stream, and supplies the bit stream passing through theanalysis back to the start code analyzer 83 (step ST32).

The VOL header analyzer 84 analyzes in the bit stream the VOL headerinformation, the object intra-coded indicator signal 7′ and the VOP rateinformation 87, and supplies the bit stream passing through the analysisback to the start code analyzer 83, the analyzed object intra-codedindicator signal 7′ to the frame skip VOP controller 86, and theanalyzed VOP rate information 87 to the decoded VOP selector 88 (stepST33).

The GOV header analyzer 61 analyzes the GOV header information in theinput bit stream, and supplies the bit stream passing through theanalysis back to the start code analyzer 83 (step ST34).

Then, the decoded VOP selector 88 compares the coding side VOP rateinformation 87 fed from the VOL header analyzer 84 with the VOP rateinformation 71 set on the decoder side by a user or the like, andsupplies the frame skip VOP controller 86 with the VOP selectinformation 89 indicating the information on the VOP to be decoded inaccordance with the compared result (step ST35).

The VOP select information 89 will be described in more detail. Assumehere that the VOP rate information 87 fed from the VOL header analyzer84 indicates 30 pieces/second, and the VOP rate information 71 set onthe decoder side is 15 pieces/second. In this case, the VOP selectinformation 89 indicates that every other VOPs are to be analyzed. Thiscorresponds to the fact that the decoder side decodes the VOPsalternately when decoding the bit stream encoded by the encoder side ata rate of 30 pieces per second.

Next, the frame skip controller 86 carries out the processing shown atsteps ST36 and ST37. The frame skip control processing will now bedescribed together with the VOP header analysis at step ST38.

First, as shown in FIG. 30, the object intra-coded decision section 73in the frame skip VOP controller 86 decides the output destination ofthe bit stream in response to the object intra-coded indicator signal 7′fed from the VOL header analyzer 84 (step ST36). More specifically, theobject intra-coded decision section 73 decides, as the outputdestination of the input bit stream, the frame skip VOP decision section91 when the object intra-coded indicator signal 7′ is ON, and the VOPheader analyzer 90 when the object intra-coded indicator signal is OFF.

When the object intra-coded indicator signal 7′ is ON, the frame skipVOP decision section 91 in the frame skip VOP controller 86 makes adecision corresponding to step ST37. Specifically, the frame skip VOPdecision section 91 makes a decision as to whether the VOP to beanalyzed is to be decoded or not in response to the VOP selectinformation 89 and count 85. When the frame skip VOP decision section 91decides that the VOP is to be decoded (“YES” at step ST37), it suppliesthe input bit stream to the VOP header analyzer 90. In contrast, when itdecides that further analysis is unnecessary (“NO” at step ST37), itsupplies the input bit stream back to the start code analyzer 83. Forexample, when the VOP select information 89 indicates that the VOPs tobe analyzed take place at every other VOP, the frame skip VOP decisionsection 91 makes a decision that the decoding is necessary when thecount 86 is an even number, and unnecessary when the count is an oddnumber.

The VOP header analyzer 90 analyzes the VOP header in the input bitstream, and supplies the bit stream after the analysis back to the startcode analyzer 83 (step ST38). The start code analyzer 83 supplies thebit stream 43 after the analysis to the video signal analyzer 44 (see,FIG. 18) when the analysis by the VOP header analyzer 90 has beencompleted.

Thus, when the object intra-coded decision section 73 of the frame skipVOP controller 86 decides that the object intra-coded indicator signal7′ is OFF at step ST36, it supplies the input bit stream to the VOPheader analyzer 90 without passing through the frame skip VOP decisionsection 91, which prevents the VOP from undergoing the frame skipping.This principle is the same as that of the foregoing embodiment 3. Incontrast, when the object intra-coded decision section 73 decides thatthe object intra-coded indicator signal 7′ is ON at step ST36, the frameskip VOP decision section 91 makes a decision as to whether the VOP tobe analyzed at present has to be decoded or not in response to the VOPselect information 89 and count 85. Then, it supplies the VOP headeranalyzer 90 with only the input bit stream to be decoded, therebycarrying out the VOP frame skipping.

As described above, the present embodiment 4 operates just as theforegoing embodiment 3 except that it has a function to carry out thedisplay control based on the result of decoding the bit stream includingthe encoder side VOP rate information 87 multiplexed into the VOL headerinformation on the encoder side. In addition, the present embodiment 4is configured such that it analyzes the object intra-coded indicatorsignal 7′ when decoding the coded bit stream including the objectintra-coded indicator signal 7′ multiplexed into the VOL header. Thismakes it possible, when the object intra-coded indicator signal 7′ isON, that is, when a decision is made that all the VOP data are intracoded, to carry out such processing as displaying the objects associatedwith these VOP data with frame skipping any desired VOPs in response toboth the VOP rate information 87 set one the encoder side and the VOPrate information 71 set on the decoder side.

Furthermore, the present embodiment 4 is configured such that it decodesthe coded bit stream 81 including the object intra-coded indicatorsignal 7′ and VOP rate information 87 in the VOL header. This enablessimpler frame skip control in addition to the advantage of the foregoingembodiment 3 of being able to perform display with frame skipping anydesired VOPs. This is because it is unnecessary for the presentembodiment 4 to analyze the individual VOP headers to decode therelative time information (modulo-time base and VOP time increment)about the display times which are set individually.

Although it is assumed in the foregoing explanation that the decodingside receives and decodes the coded bit stream including the encoderside VOP rate information multiplexed into the VOL header, the presentinvention is not limited to this. For example, a coded bit stream can bedecoded that has the encoder side VOP rate information multiplexed intothe GOV header. This is implemented by providing a GOV header analyzer92 in the header analyzer 42 with the function to decode encoder sideVOP rate information 93 as shown in FIG. 32. Thus, the VOP rateinformation 93 becomes the information indicating the VOP display ratein the GOV.

Furthermore, as the foregoing embodiment 3, the present embodiment 4 canbe configured such that it handles a bit stream including the objectintra-coded indicator signal 7′ encoded on every GOV basis, withoffering a similar effect. In this case, in FIG. 29, not the VOL headeranalyzer 84 but the GOV header analyzer 61 has a function to analyze theobject intra-coded indicator signal 7′, and in FIG. 32, not the VOLheader analyzer 75 but the GOV header analyzer 92 has the function toanalyze the object intra-coded indicator signal 7′, for example.

Moreover, the present embodiment 4 can achieve an advantage similar tothat of the foregoing embodiment 3 by applying the VOP decoder of thepresent embodiment 4 to the system for decoding and combining aplurality of objects as shown in FIG. 27 described in connection withthe embodiment 3. This holds true for the VOP decoders of otherembodiments which will be described later. Thus, the followingembodiments can also be applied to configure the system for decoding andcombining a plurality of objects as shown in FIG. 27.

Embodiment 5

The embodiment 5 in accordance with the present invention relates to animage decoding apparatus capable of carrying out decoding and displayingVOPs at random at any desired time by receiving a coded bit stream thatincludes in a VOL layer the object intra-coded indicator signal, andincludes in a GOV layer the time code information representing theabsolute display time of the VOP at the initial position of the GOV.Since the present embodiment 5 differs from the decoding apparatus ofthe embodiment 3 in only the configuration of the header analyzer 42,only the configuration and operation of the header analyzer 42 will bedescribed. Besides, in the present embodiment 5, the decoder will bedescribed that receives and decodes the coded bit stream 30 as shown inFIG. 8.

FIG. 33 shows a configuration of the header analyzer 42 in theembodiment 5 in accordance with the present invention. In FIG. 33, thereference numeral 94 designates a start code analyzer; 95 designates astoring medium for storing the coded bit stream 30 transmitted from thecoding side, such as a memory like a DRAM or SRAM, or a disk driveconnected to a PC; 96 designates a VOP header analyzer; 97 designates anexternally set time code; 98 designates a frame skip controller; and 99designates a search instruction signal.

FIG. 34 shows a configuration of the frame skip controller 98 as shownin FIG. 33. In FIG. 34, the reference numeral 73 designates the objectintra-coded decision section; 100 designates a comparator; and 101designates a storing medium.

Next, the operation of the header analyzer 42 of the present embodiment5 will be described.

FIG. 35 is a flowchart illustrating the operation of the header analyzer42 of the present embodiment 5.

In the header analyzer 42 of the present embodiment 5, the start codeanalyzer 94 analyzes the start code included in the input coded bitstream 30 (step ST39). The start code analyzer 94 supplies the bitstream to the VO header analyzer 59 when the analyzed start codeindicates a VO (step ST40), to the VOL header analyzer 60 when theanalyzed start code indicates a VOL (step ST41), to the GOV headeranalyzer 61 when the analyzed start code indicates a GOV (step ST42),and to the VOP header analyzer 96 when the analyzed start code indicatesa VOP (step ST43). Incidentally, after completing the analysis by theVOP header analyzer 96, the bit stream is supplied to the video signalanalyzer 44, and the processing is returned to the start code analysisagain when the video signal analyzer completes the analysis and decodingof the video signal of the current VOP.

The VO header analyzer 59 analyzes the VO header information in theinput bit stream, and supplies the start code analyzer 94 with the bitstream after the analysis (step ST44).

The VOL header analyzer 60 analyzes the VOL header information in theinput bit stream, and supplies the start code analyzer 94 with the bitstream after the analysis (step ST45). In the course of this, the VOLheader analyzer 60 decodes the object intra-coded indicator signal 7′contained in the VOL header, and supplies it to the VOP header analyzer96.

The GOV header analyzer 61 analyzes the GOV header information in theinput bit stream, and supplies the start code analyzer 94 with the bitstream after the analysis (step ST46). In the course of this, GOV headeranalyzer 61 decodes the time code 63 in the GOV header information, andsupplies it to the VOP header analyzer 96.

The VOP header analyzer 96, which carries out the VOP header analysis atstep ST47, comprises a structure for achieving high rate, simple randomaccess of the VOP disclosed in the present embodiment 5. The structureis implemented by the frame skip controller 98.

FIG. 36 is a flowchart illustrating the processing in the VOP headeranalysis at step ST47 by the frame skip controller 98. Referring to FIG.33 showing the details of the VOP header analyzer together with FIGS. 34and 36, the VOP random access processing will be described.

First, as operation environments, the following conditions (1)-(4) areassumed.

(1) The decoding and display of objects is carried out by reading andloading the coded bit stream stored in the storing medium 95 (such as astorage like a CD-ROM and DVD, a memory like a DRAM and SDRAM, and ahard disk drive connected to a PC). In this case, the time codes areeach displayed on the display screen in synchronism with the VOP displayto notify the user of the absolute display time of respective VOPs. Thecoded bit stream can be transferred from the decoder to the readablestoring medium 95 through a network or broadcasting network.

(2) The user stops the decoding at any desired position. At the sametime, the tine code also halts at the corresponding VOP. The displaycontinues showing the last VOP image displayed just before halting thedecoding. It is assumed that the user wishes to extract from the bitstream a VOP image at a position before or after the stopped position asa still picture.

(3) The user inputs the time code of the VOP image he or she wished toextract by such a means as a command designating the time code or thelike. The input time code thus entered becomes the externally set timecode 97.

(4) Comparing the externally set time code 97 input by the user at theforegoing stage (3) with the time code of the currently stopped VOPimage. If they differ from each other, the VOP image with the time codematching the externally set time code 97 is searched for and is decodedand displayed.

Incidentally, since each VOP usually undergoes predictive coding usingVOP images before and after its position, all the VOPs having predictiverelevance must be decoded before reaching the VOP with the desired timecode to achieve the foregoing operation.

In the present embodiment 5, however, using the object intra-codedindicator signal 7′ and the frame skip controller 98 makes it possibleto immediately infer the VOL that is intra coded, that is, undergonecoding without prediction, and as for such a VOL header, to decode andregenerate the desired VOP picture by directly searching for it.

First, in the foregoing condition (1), the decoding apparatus carriesout the normal decoding operation. Assume that the decoding apparatus isin transition from the foregoing condition (1) to (2). In this state,the time code of the VOP image to be stopped is calculated. Thecalculation consists of three steps (step ST47-1-S47-3).

The first step analyzes the modulo-time base in the bit stream (stepST47-1), which is carried out by the modulo-time base analyzer 64.

The second step analyzes the VOP time increment in the bit stream (stepST47-2), which is carried out by the VOP time increment analyzer 67.

The third step calculates the VOP time code 70 indicating the decodedVOP absolute display time from the modulo-time base, VOP time incrementand the GOV time code 63 fed from the GOV header analyzer 61 (stepST47-3). This is carried out by the decoded VOP absolute display timegenerator 66, and its calculation method was described in the foregoingembodiment 3. The VOP time code at the halt state of the foregoingcondition (2) is exhibited to the user.

Subsequently, the user carries out the operation (3). This will providesthe externally set time code 97, enabling the random access mechanism bythe frame skip controller 98.

More specifically, the comparator 100 makes a decision as to whether thecurrent VOP is the VOP a user wishes to display or not (step ST47-4) bycomparing the time code of the VOP the user wishes to display, that is,the externally set time code 97 with the VOP time code 70 of thecurrently displayed VOP.

If they agree with each other, a decision is made that it is the “VOP tobe displayed” (“YES” at step ST47-4), enabling the video informationheader analysis (step ST47-11). If not (“NO” at step ST47-4), a decisionis made as to whether the VOP to be displayed is previous to the currentVOP or not by comparing the externally set time code 97 with the VOPtime code 70 of the current VOP (step ST47-5). Thus, one of thefollowing two cases 1 and 2 is decided. In the course of this, thestoring medium 101 temporarily stores the VOP time codes 70 previouslyused during the comparison by the comparator 100 so that the comparator100 can select the VOP time code 70 close to the externally set timecode 97.

Case 1:

The case 1 takes place when the externally set time code 97 indicates atime subsequent to the VOP time code 70 in the foregoing condition (2)such as the externally set time code 97 is 01:00:30, and the VOP timecode 70 in the condition (2) is 01:00:10 (“YES” at step ST47-5). Theaction is switched in response to the value of the object intra-codedindicator signal 7′ (step ST47-6).

More specifically, when the object intra-coded indicator signal 7′ is ON(“NO” at step ST47-6), that is, when it indicates that “all the VOPs inthe VOL are intra coded”, the comparator 100 sets the search instructionsignal 99 to “forward search”, and sends it with the bit stream to thestart code analyzer 94 (step ST47-7). Thus, the start code analyzer 94searches for the VOP start code ahead of, that is, after the VOP timecode 70 in the condition (2).

In contrast, when the object intra-coded indicator signal 7′ is OFF(“YES” at step ST47-6), that is, when it indicates that “the VOPs in theVOL are subject to the predictive coding”, the individual VOPs cannot bedirectly decoded because they undergo the predictive coding. In thiscase, the VOP time code 70 is calculated by decoding the modulo-tinebase 65 and VOP time increment 68 of the individual VOPs through theforegoing steps ST47-1-47-3 and ST47-11, so that the individual VOPimages are decoded sequentially. Thus, the subsequent VOPs aresuccessively decoded in this case.

Case 2:

The case 2 takes place when the externally set time code 97 indicates atime before the VOP time code 70 in the foregoing condition (2) such asthe externally set time code 97 is 01:00:00, and the VOP time code inthe foregoing condition (2) is 01:00:10 (“NO” at step ST47-5). Theaction is switched in response to the value of the object intra-codedindicator signal 7′ (step ST47-8).

More specifically, when the object intra-coded indicator signal 7′ is ON(“NO” at step ST47-8), that is, when “all the VOPs in the VOL are intracoded”, the comparator 100 sets the search instruction signal 99 at“backward search”, and sends it together with the bit stream to thestart code analyzer 94 (step ST47-9). This makes it possible for thestart code analyzer 94 to analyze the bit stream in the backwarddirection, thereby enabling searching for the start code of the VOPsbefore the foregoing condition (2).

In contrast, when the object intra-coded indicator signal 7′ is OFF(“YES” at step ST47-8), that is, when it indicates that “the VOPs in theVOL are subject to the predictive coding”, the individual VOPs cannot bedirectly decoded because they undergo the predictive coding. In thiscase, the VOP time code 70 must be calculated by decoding themodulo-time base 65 and VOP time increment 68 of the individual VOPs,and the image data twist be decoded by ascending to the VOP images thatare not subjected to the prediction, that is, to the previous I-VOP(intra-coded VOP), and by restarting the decoding therefrom. This ishandled by instructing to perform backward search by ascending to theprevious I-VOP according to the search instruction signal 99 (stepST47-10).

Thus, in the present embodiment 5, when the object intra-coded indicatorsignal 7′ is ON in the cases 1 and 2, the start code detection of theVOPs is continued according to the search instruction signal 99, and theVOP image data is skipped without carrying out the video informationheader analysis at step ST47-11.

Specifically, every time the VOP start code is detected, the followingprocessings are iterated until the externally set time code 97 agreeswith the VOP time code 70 obtained as a result of the search. Theseprocessings comprise the analysis of the modulo-time base and VOP timeincrement of the individual VOPs; the calculation of the VOP time code70 indicating the absolute display time of the currently decoded VOP(step ST47-1-S47-3); and a decision making as to whether the current VOPis a VOP to be displayed or not by comparing the current VOP time code70 with the externally set time code 97 (step ST47-4). These processingsare iterated until the externally set time code 97 agrees with the VOPtime code 70 obtained as a result of the search. When the externally settime code 97 agrees with the VOP time code 70 as a result of the search,which means that the decoding is stopped at the exact position of theVOP to be displayed, the operation of the random access is completed.

As described above, according to the present embodiment 5, when theobject intra-coded indicator signal 7′ that indicates whether all theVOPs in the VOL are intra coded or not is ON, that is, when all the VOPsin the VOL are intra coded, the VOP image data is skipped withoutperforming the sequential decoding of individual VOPs based on the videoinformation header analysis at step ST47-11 so that the desired VOPimage data is directly searched for and decoded.

As a result, considering a home video according to the MPEG-4compression standard, which intra codes all VOPs and stores them on thestoring medium 95, and edits a desired scene by combining them withother object videos provided through the Internet or by means of aCD-ROM or DVD-ROM, the decoding apparatus with the configuration of thepresent embodiment 5 can make a high speed access to a picture at adesired time in the video pictures acquired, thereby enabling the videoedition without stress.

Furthermore, the video contents can be stored in a large capacityrecording medium such as a DVD-RAM with their VOPs being intra codedusing the compression standard according to the MPEG-4, so that desirededition can be achieved by exploiting high speed access when producing atelevision program.

Although the present embodiment 5 is described by way of example of thecoded bit stream 30 including the object intra-coded indicator signal 7′multiplexed into the VOL header as shown in FIG. 8, in which the bitstream containing the GOV layer including the time code is decoded, thepresent invention is not limited to this. For example, as for the codedbit stream 31 as shown in FIG. 9 that includes the object intra-codedindicator signal 7′ multiplexed into the GOV header 31 c, random accessto a desired VOP can be made smoothly using the configuration thatanalyzes the object intra-coded indicator signal 7′ by the GOV headeranalyzer 61 when all the VOP in the GOV are intra coded.

Embodiment 6

In the present embodiment 6 in accordance with the present invention, animage decoding apparatus will be described which receives a coded bitstream, and can perform decoding and display by randomly designating theVOP at a desired time. The coded bit stream includes in the VOL layerthe object intra-coded indicator signal 7′ and the VOP rate informationas the display rate information indicating the display rate of the VOPsin the VOL, and includes in the GOV layer the time code informationrepresenting the absolute display time of the VOP at the initialposition of the GOV. In the present embodiment 6, since only theconfiguration of the header analyzer of the decoding apparatus differsfrom that of the embodiment 4, only the operation of the header analyzerwill be described below. Besides, it is assumed in the followingdescription of the present embodiment 6 that the coded bit stream 81 asshown in FIG. 28 is input and decoded.

FIG. 37 is a block diagram showing a configuration of the headeranalyzer 42 in the embodiment 6 in accordance with the presentinvention. In FIG. 6, the reference numeral 102 designates a start codeanalyzer; 103 designates a decoded VOP selector; and 104 designates aVOP header analyzer. Since the remaining configuration is the same asthat of the header analyzer as shown in FIG. 29 of the embodiment 4, thedescription thereof is omitted here by assigning the same referencenumerals.

FIG. 38 shows an internal configuration of the decoded VOP selector 103as shown in FIG. 37. In FIG. 38, the reference numeral 73 designates anobject intra-coded decision section; 100 designates a comparator; and105 designates a VOP time code calculating section.

Next, the operation of the header analyzer 42 of the present embodiment6 will be described.

FIG. 39 is a flowchart illustrating the operation of header analyzer 42of the present embodiment 6.

In the header analyzer 42 of the present embodiment 6, the start codeanalyzer 102 analyzes the start code contained in the input coded bitstream 81 (step ST48), first. The start code analyzer 102 supplies thebit stream to the VO header analyzer 59 when the analyzed start coderepresents the VO (step ST49), to the VOL header analyzer 84 when theanalyzed start code represents the VOL (step ST50), to the GOV headeranalyzer 61 when the analyzed start code indicates the GOV (step ST51),and to the decoded VOP selector 103 when the analyzed start codeindicates the yap (step ST52).

After completing the analysis, the VOP header analyzer 104 supplies thebit stream 43 passing through the header analysis to the video signalanalyzer 44 which analyzes and decodes the video signal of the currentVOP, and the processing returns to the start code analysis, again. Thestart code analyzer 102 has a VOP counter in its inside, whichincrements the VOP count every time the VOP start code is detected, andoutputs the count 85. The count 85 is supplied to the decoded VOPselector 103. It is assumed here that the count 85 is reset every timethe GOV start code or VOL start code is detected.

The VO header analyzer 59 analyzes VO header information in the inputbit stream, and supplies the bit stream after the analysis to the startcode analyzer 102 (step ST53).

The VOL header analyzer 84 analyzes the VOL header information in theinput bit stream, and supplies the bit stream after the analysis to thestart code analyzer 102 (step ST54). In the course of this, the VOLheader analyzer 84 decodes the object intra-coded indicator signal 7′and VOP rate information 87 contained in the VOL header information, andsupplies them to the decoded VOP selector 103.

The GOV header analyzer 61 analyzes the GOV header information in theinput bit stream, and supplies the bit stream after the analysis to thestart code analyzer 102 (step ST55).

In the course of this, the GOV header analyzer 61 decodes the GOV timecode 63 contained in the GOV header information, and supplies it to thedecoded VOP selector 103.

Thus, the decoded VOP selector 103 can implement the high speed, simpleVOP random access structure disclosed by the present embodiment 6 (stepST56).

According to the present embodiment 6, using the object intra-codedindicator signal 7′ and the decoded VOP selector 103 makes it possibleto immediately infer the VOL intra coded, that is, the VOL undergonecoding without prediction, and as for such a VOL header, to decode andregenerate the desired VOP picture by directly searching for it.

In particular, in the present embodiment 6, the VOL layer contains theVOP rate information, and the time codes 70 of the individual VOPs canbe identified without decoding the modulo-time base and VOP timeincrement.

FIG. 40 is a flowchart illustrating the detail processing of the VOPrandom access by the decoded VOP selector 103 at step ST56.

Referring mainly to FIGS. 38 and 40, the operation of the VOP randomaccess processing will be described. Here, assume the conditions (1)-(4)described in the foregoing embodiment 5 as the operation conditions.

More specifically, the decoding apparatus carries out the normaldecoding operation in the condition (1) in the present embodiment 6.Assumed that the decoding apparatus is in a transition from thecondition (1) to the condition (2). In this case, the VOP time codecalculating section 105 first calculates the time code 70 of the VOPimage whose decoding is to be halted in response to the user action inthe condition (2) (step ST56-1). It is obtained by the followingexpression.VOP time code 70=GOV time code 63+(count 85)+(VOP rate information 87)

In other words, the VOP time code calculating section 105 divides thecount 85 by the VOP rate information 87 on the coding side, and adds thequotient to the GOV time code 63 to obtain the time code 70 of the VOPimage whose decoding is to be halted.

For example, when the GOV time code 63 is 01 hour 00 minute 00 second,the count 85 is 60, and the coding side VOP rate information 87 is 30pieces/second, the VOP time code is calculated as 01 hour 00 minutes 02seconds by adding 60/30 (=2) seconds to the GOV time code 63.

According to the present embodiment 6, it is unnecessary to obtain theVOP time code 70 of the VOP image for halting the decoding through thethree steps (step ST47-1-ST47-3) as in the foregoing embodiment 5.Instead of this, the start code analyzer 102 detects the start code ofeach VOP, and increments the VOP counter so that it can decide, usingthe count 85, the VOP rate information 87 on the coding side and the GOVtime code 63, the VOP time code 70 for halting the decoding more quicklythan the embodiment 5 can do. Thus, it can presents the user with theVOP time code at the halt state in the foregoing condition (2).

Subsequently, the user carries out the operation in the foregoingcondition (3), which will provide the externally set time code 97 theuser wishes to extract. This will activate the random access structureby the decoded VOP selector 103.

More specifically, the comparator 100 decides first on whether the VOPat which the decoding is halted is the VOP the user wishes to display ornot (step ST56-2) by comparing the externally set time code 97 with theVOP time code 70 fed from the VOP time code calculating section 105.

When they agree (“YES” at step ST56-2), the comparator 100 decides thatthe VOP is the “VOP to be displayed”, and carries out the analysis ofthe VOP header (step ST57). Otherwise (“NO” at step ST56-2), comparingthe externally set time code 97 with the VOP time code 70 of the currentVOP, it decides as to whether the VOP to be displayed is before or afterthe current VOP (step ST56-3), and then makes a decision on which one ofthe following cases 1 and 2 applies.

Case 1:

The case 1 applies when the externally set time code 97 indicates thatit follows the VOP time code 70 in the foregoing condition (2) such aswhen the externally set time code 97 is 01:00:30, and the VOP time code70 in the foregoing condition (2) is 01:00:10 (“YES” at step ST56-3). Inthis case, the action to be taken is switched in response to the valueof the object intra-coded indicator signal 7′ (step ST56-4).

Thus, when the object intra-coded indicator signal 7′ is ON (“NO” atstep ST56-4), that is, when it indicates that “all the VOPs in the VOLare intra coded”, the comparator 100 places the search instructionsignal 99 at “forward search”, and supplies it together with the bitstream to the start code analyzer 102 (step ST56-5).

This enables the start code analyzer 102 to search for the VOP startcode forward, that is, the VOP start code subsequent to the VOP timecode 70 at which the decoding is halted in the foregoing condition (2).

On the contrary, when the object intra-coded indicator signal 7′ is OFF(“YES” step ST56-4), that is, when it indicates that the “VOPs in theVOL undergo the predictive coding”, the individual VOPs cannot bedirectly decoded because the VOPs in the VOL are predictively coded.

Accordingly, the VOP header analyzer 104 must carry out in the normalVOP header analysis at the next step ST57 substantially the sameprocessing as that of steps ST47-1-ST47-3 and ST47-11 as shown in FIG.36 to analyze and decode the individual VOP modulo-time base and VOPtime increment, and to calculate the VOP time code 70 of the current VOPat which the decoding is halted in order to successively decode the VOPimages. Thus, the next VOP is sequentially decoded in this case.

Case 2:

The case 2 applies when the externally set time code 97 indicates thatit precedes the VOP time code 70 in the foregoing condition (2) such aswhen the externally set time code 97 is 01:00:00 and the VOP time code70 in the foregoing condition (2) is 01:00:10 (“NO” at step ST56-3). Inthis case, the action to be taken is switched in response to the valueof the object intra-coded indicator signal 7′ (step ST56-6).

Thus, when the object intra-coded indicator signal 7′ is ON (“NO” atstep ST56-6), the comparator 100 places the search instruction signal 99at “backward search”, and supplies it together with the bit stream tothe start code analyzer 102 (step ST56-7).

This enables the start code analyzer 102 to start analyzing the bitstream in the reverse direction, and to search the VOP start codeprevious to the foregoing condition (2).

On the contrary, when the object intra-coded indicator signal 7′ is OFF(“YES” step ST56-6), that is, when it indicates that the “VOPs in theVOL undergo the predictive coding”, the individual VOPs cannot bedirectly decoded because the VOPs in the VOL undergo the predictivecoding. In this case, the individual VOP image data must be decoded bytracing back to the VOP image that does not undergo the predictivecoding, that is, to the previous I-VOP, and the decoding must berestarted therefrom. This is achieved by the search instruction signal99 that instructs to trace back to the previous I-VOP with carrying outthe reverse search (step ST56-8).

Thus, in the present embodiment 6, when the object intra-coded indicatorsignal 7′ is ON in the cases 1 and 2, the start code detection of theVOPs is continued according to the search instruction signal 99, and theVOP image data is skipped without the video information header analysisat step ST57.

Specifically, every time the VOP start code is detected, the followingprocessings are iterated until the externally set time code 97 agreeswith the VOP time code 70 obtained as a result of the search. Theseprocessings comprise the calculation of the VOP time code 70 indicatingthe absolute display time of the current VOP (step ST56-1); and adecision making as to whether the current VOP is a VOP to be displayedor not by comparing the current VOP time code 70 with the externally settime code 97 (step ST56-2). Then, when the externally set time code 97agrees with the VOP time code 70 as a result of the search, which meansthat the decoding is stopped at the exact position of the VOP to bedisplayed, the operation of the random access is completed.

As described above, according to the present embodiment 6, when theobject intra-coded indicator signal 7′ that indicates whether all theVOPs in the VOL are intra coded or not is ON, that is, when all the VOPsin the VOL are intra coded, the sequential VOP decoding is skippedwithout performing the VOP header analysis for individual VOPs at stepST57. This enables the desired VOP image data to be directly searchedfor and decoded.

Furthermore, in the present embodiment 6, the VOP time code 70 isdetermined using the GOV time code 63 which is the time code of theinitial VOP of the GOV, the count 85 fed from the start code analyzer102 and the VOP rate information 87 on the coding side. This obviatesthe need for decoding the modulo-time base or VOP time incrementinformation for each VOP, which means that random access can be achievedby calculating in advance the number of VOPs to be skipped from theexternally set time code 97. Thus, the present embodiment 6 can dispensewith the need for successively calculating the display time of each VOPto make the decision at steps ST47-1-ST47-3 of FIG. 36 as in theforegoing embodiment 5. This enables the random access faster than thatof the embodiment 5. In brief, high-speed random access is implementedbecause the individual VOP time code can be identified from the VOP rateinformation without calculating the display time of each VOP withperforming the successive VOP header analysis.

For example, considering a home video according to the MPEG-4compression standard, which intra codes all VOPs and stores them on thestoring medium 95 and edits a desired scene by combining them with otherobject videos provided through the Internet or by means of a CD-ROM orDVD-ROM, the decoding apparatus with the configuration of the presentembodiment can make a high speed access to a picture at a desired timein the video pictures acquired, thereby enabling the video editionwithout stress. Furthermore, the video contents can be stored in a largecapacity recording medium such as DVD-RAM with their VOPs being intracoded by the compression standard according to the MPEG-4, so thatdesired edition can be achieved by making high speed access whenproducing a television program.

Although the present embodiment 6 is described by way of example of thecoded bit stream 81 as shown in FIG. 28, which not only includes theobject intra-coded indicator signal 7′ and VOP rate information 87multiplexed into the VOL header 81 b, but also includes in the GOVheader 81 c the GOV tine code 63 indicating the absolute display time ofthe initial VOP in the GOV, the present invention is not limited tothis. For example, a coded bit stream (not shown) can be decoded whichincludes in the GOV header not only the GOV time code 63, but also theobject intra-coded indicator signal 7′ and VOP rate information 87. Thisis implemented by providing the GOV header analyzer 61 as shown in FIG.37 with the decoding function of the object intra-coded indicator signal7′ and VOP rate information 87, in addition to the decoding function ofthe GOV time code 63.

Embodiment 7

In the present embodiment 7 in accordance with the present invention, aVOP decoder will be described for decoding the coded bit streamgenerated by the VOP encoder of the foregoing embodiment 2.

Thus, the VOP decoder of the present embodiment 7 is characterized inthat it receives the coded bit stream 39 as shown in FIG. 15, decodesfrom the coded bit stream 39 the object intra-coded indicator signal 7′,the display time multiplex identification information 34 and the timecodes 35 of individual VOPs described in the embodiment 2, and controlsthe decoding and display of the VOPs in accordance with these values.

The VOP decoder in the present embodiment 7 has substantially the sameconfiguration as the VOP decoder described in the embodiment 6, exceptfor the header analyzer 42. Accordingly, only the header analyzer 42 ofthe present embodiment 7 will be described below.

FIG. 41 is a block diagram showing an internal configuration of theheader analyzer 42 in the present embodiment 7. In FIG. 41, thereference numeral 106 designates a VOL header analyzer; and 107designates a decoded VOP selector. Since the remaining configuration isthe same as that of the header analyzer 42 of the embodiment 6 as shownin FIG. 37, the description thereof is omitted here by assigning thesame reference numerals.

FIG. 42 is a block diagram showing an internal configuration of thedecoded VOP selector 107 of the present embodiment 7 as shown in FIG.41. In FIG. 42, the reference numeral 73 designates an objectintra-coded decision section; 100 designates a comparator; and 108designates a VOP time code holder.

The operation of the header analyzer 42 of the present embodiment 7 willnow be described.

FIG. 43 is a flowchart illustrating the operation of the header analyzer42 of the present embodiment 7.

In the header analyzer 42 of the present embodiment 7, the start codeanalyzer 102 analyzes the start code contained in the input coded bitstream 39, first (step ST58). The start code analyzer 102 supplies thebit stream to the VO header analyzer 59 when the analyzed start codeindicates a VO (step ST59); to the VOL header analyzer 106 when theanalyzed start code indicates a VOL (step ST60); to the GOV headeranalyzer 61 when the analyzed start code indicates the GOV (step ST61);and to the decoded VOP selector 107 when the analyzed start codeindicates the VOP (step ST62).

Incidentally, when the VOP header analyzer 104 completes its analysis,the start code analyzer 102 supplies the bit stream 43 to the videosignal analyzer 44, so that the video signal analyzer 44 carries out theanalysis and decoding of the video signal of the current VOP, andreturns the processing to the start code analysis, again. The start codeanalyzer 102 includes a VOP counter that increments the VOP count everytime the VOP start code is detected, and supplies the count 85 to thedecoded VOP selector 107. It is assumed here that the VOP counter isreset every time the VOL start code is detected.

The VO header analyzer 59 analyzes VO header information in the inputbit stream, and supplies the bit stream after the analysis back to thestart code analyzer 102 (step ST63).

The VOL header analyzer 106 analyzes the VOL header information in theinput bit stream, and supplies the bit stream after the analysis back tothe start code analyzer 102 (step ST64).

In the course of this, the VOL header analyzer 106 decodes the objectintra-coded indicator signal 7′, the display time multiplexidentification information 34 and the time codes 35, which are containedin the VOL header information as shown in FIG. 15, and supplies them tothe decoded VOP selector 107.

As described in the foregoing embodiment 2, the display time multiplexidentification information 34 is decoded only when the objectintra-coded indicator signal 7′ is ON, that is, only when it indicatesthat all the VOPs contained in the VOL unit is intra-coded, and the timecodes 35 are decoded only when the display time multiplex identificationinformation 34 is also ON. Assume here that both the object intra-codedindicator signal 7′ and display time multiplex identificationinformation 34 are ON, and the time codes 35 of all the VOPs in the VOLare decoded by the VOL header analyzer 106.

The GOV header analyzer 61 analyzes the GOV header information in theinput bit stream, and supplies the bit stream after the analysis back tothe start code analyzer 102 (step ST65).

In the course of this, although the GOV header analyzer 61 decodes theGOV time code 63 contained in the GOV header information, the presentembodiment 7 does not use the GOV time code information.

The decoded VOP selector 107, which has the high speed, simple andrandom access structure of the VOP disclosed in the present embodiment7, selects the VOP to be decoded (step ST66). The random accessmechanism of the present embodiment 7 is characterized in that it canobtain the VOP time codes to be compared with the externally set timecode 97 by the comparator 100 without any calculation.

FIG. 44 is a flowchart illustrating the processing in detail of the VOPrandom access structure based on the decoded VOP selection at step ST66by the decoded VOP selector 107.

With reference to FIGS. 42 and 44 mainly, the operation of the VOPrandom access processing will be described, in which the foregoingconditions (1)-(4) described in the embodiment 5 are also assumed as theoperation conditions.

First, the time codes 35 of all the VOPs in the VOL decoded by the VOLheader analyzer 106 are stored in the VOP time code holder 108 in theVOP selector 107 to be retained until the decoding of the VOL iscompleted (step ST66-1). In the condition (1), the decoding apparatuscarries out normal decoding operation, here.

Assume the instant at which the decoding apparatus makes a transitionfrom the condition (1) to condition (2).

In response to the transition from the condition (1) to condition (2) bythe user operation, the VOP time code holder 108 in the decoded VOPselector 107 receives or generates a read command (not shown) forreading the time code 35 of the VOP image pointed by the count 85 at thetransition.

In response to this, the VOP time code holder 108 reads as the VOP timecode 70 the VOP pointed by the count 85 fed from the start code analyzer102 at the instant of the transition from the condition (1) to condition(2), that is, the time code 35 of the VOP image at the time the decodingis to be halted in accordance with the condition (2), and supplies theVOP time code 70 to the comparator 100 (step ST66-2).

In this way, the foregoing structure can identify the VOP time code 70at the time the decoding is to be halted in the condition (2) only fromthe count 85 fed from the start code analyzer 102 without carrying outany analysis of the VOP header or any calculation. Thus, the VOP timecode 70 in the stop condition (2) is presented to the user.

Next, when the user carries out the condition (3), this will provide theexternally set time code 97 to the comparator 100, and activate therandom access structure by the decoded VOP selector 107.

Although in the example above, the VOP time code holder 108 is describedsuch that it supplies the comparator 100 with the time code 35 of theVOP image pointed by the count 85 fed at the transition to the condition(2) as the VOP time code 70, this is not essential. For example, The VOPtime code holder 108 can always supply the comparator 100 with the timecode 35 of the VOP image, which is pointed by the count 85 constantlyfed from the start code analyzer 102, as the VOP time code 70. However,in the latter case, the comparator 100 must be configured such that itimplements the random access structure using the VOP time code 70 fed atthe instant of the transition to the condition (2) and the externallyset time code 97 fed by the operation of the condition (3). In brief, itis enough for the random access structure to operate such that itutilizes among the time codes 35 stored in the VOP time code holder 108the VOP time code 70 at the transition to the condition (2) and theexternally set time code 97.

More specifically, the comparator 100 first makes a decision as towhether the current VOP is the VOP the user wishes to display or not(step ST66-3) by comparing the externally set time code 97 with the VOPtime code 70 of the current VOP which is fed from the VOP time codeholder 108 and takes place at the time the decoding is halted inaccordance with the condition (2).

When the externally set time code 97 agrees with the VOP time code 70 ofthe current VOP (“YES” step ST66-3), the VOP is decided as the “VOP tobe displayed”, followed by the VOP header analysis of the VOP to bedisplayed (step ST67). Otherwise (“NO” at step ST66-3), a decision ismade as to whether the VOP to be displayed is previous to the currentVOP or not by comparing the externally set time code 97 with the VOPtime code 70 of the current VOP (step ST66-4). Thus, one of thefollowing two cases 1 and 2 is decided.

Case 1:

The case 1 applies when the externally set time code 97 indicates a timesubsequent to the VOP time code 70 in the foregoing condition (2) suchas the externally set time code 97 is 01:00:30, and the VOP time code 70in the condition (2) is 01:00:10 (“YES” at step ST66-4). The action isswitched in response to the value of the object intra-coded indicatorsignal 7′ (step ST66-5).

More specifically, when the object intra-coded indicator signal 7′ is ON(“NO” at step ST66-5), that is, when it indicates that “all the VOPs inthe VOL are intra coded”, the comparator 100 sets the search instructionsignal 99 to “forward search”, and sends it with the bit stream to thestart code analyzer 102 (step ST66-6). Thus, the start code analyzer 102searches for the VOP start code behind, that is, after the VOP time code70 in the condition (2).

In contrast, when the object intra-coded indicator signal 7′ is OFF(“YES” at step ST66-5), that is, when it indicates that “the VOPs in theVOL are subject to the predictive coding”, the individual VOPs cannot bedirectly decoded because they undergo the predictive coding.

Accordingly, as in the foregoing embodiment 6, the VOP header analyzer104 must carry out the processing corresponding to that of the stepsST47-1-47-3 and ST47-11 as shown in FIG. 36 in the normal VOP headeranalysis at the next step ST67 so as to analyze and decide themodulo-time base and VOP time increment of the individual VOPs and tosuccessively decode the VOP images by calculating the VOP time code 70of the current VOP at which the decoding is halted. Thus, in this case,the subsequent VOPs are sequentially decoded.

Case 2:

The case 2 takes place when the externally set time code 97 indicates atime before the VOP time code 70 in the condition (2) such as theexternally set time code 97 is 01:00:00, and the VOP time code in thecondition (2) is 01:00:10 (“NO” at step ST66-4). The action is switchedin response to the value of the object intra-coded indicator signal 7′(step ST66-7).

More specifically, when the object intra-coded indicator signal 7′ is ON(“NO” at step ST66-7), the comparator 100 sets the search instructionsignal 99 at “backward search”, and sends it with the bit stream to thestart code analyzer 102 (step ST66-8).

This makes it possible for the start code analyzer 102 to analyze thebit stream in the backward direction, thus enabling searching for thestart code of the VOPs previous to the foregoing condition (2).

In contrast, when the object intra-coded indicator signal 7′ is OFF(“YES” at step ST66-7), that is, when it indicates that “the VOPs in theVOL are subject to the predictive coding”, the individual VOPs cannot bedirectly decoded. In this case, the decoding must be continued to theimage data successively. Specifically, the decoding must be carried outby ascending to the VOP image that is not subjected to the prediction,that is, to the previous I-VOP, and be restarted therefrom. This ishandled by instructing to perform the backward search by ascending tothe previous I-VOP using the search instruction signal 99 (step ST66-9).

Thus, in the present embodiment 7, when the object intra-coded indicatorsignal 7′ is ON in the cases 1 and 2, the VOP start code detection iscontinued according to the search instruction signal 99, and the VOPimage data is skipped without carrying out the VOP header analysis atstep ST57 as in the embodiment 6.

In summary, in the present embodiment 7, because the VOP time codeholder 108 stores the time codes 35 of all the VOPs in the VOL decodedby the VOL header analyzer 106 through the processing at step ST66-1until the decoding of the current VOL is completed, every time thedecoding is halted by the user operation in the condition (2), the VOPtime code holder 108 reads the time code 35 of the VOP pointed by thecurrent count 85 as the VOP time code 70 (step ST66-2); and a decisionis made as to whether the current VOP is a VOP to be displayed or not bycomparing the VOP time code 70 with the externally set time code 97(step ST66-3). These processings are iterated until the externally settime code 97 agrees with the VOP time code 70 obtained as a result ofthe search. Then, when the externally set time code 97 agrees with theVOP time code 70 as a result of the search, which means that thedecoding stops at the VOP to be displayed, the operation of the randomaccess is completed.

As described above, according to the present embodiment 7, when theobject intra-coded indicator signal 7′, which indicates whether all theVOPs in the VOL are intra coded or not, is ON, that is, when all theVOPs in the VOL are intra coded, the desired VOP image data is directlysearched for and decoded. This is because the VOP header analysis forrespective VOPs at step ST67 can be omitted, and hence it is unnecessaryto carry out the sequential VOP decoding.

Furthermore, the present embodiment 7 is configured such that itdirectly decodes the time codes 35 in the VOPs from the VOL header, andstores them in the VOP time code holder 108 so that they are read inaccordance with the count 85 fed from the start code analyzer 102. Thismakes it possible to dispense with the need for decoding the informationabout the modulo-time base and VOP time increment, and hence the decoderdoes not require any calculation structure. Thus, the VOP to be decodedcan be identified only by comparing the externally set time code 97 witheach of the time codes 35 stored. This offers an advantage of being ableto implement a very high speed random access that is faster than thoseof the embodiments 5 and 6.

For example, considering a home video according to the MPEG-4compression standard, which intra codes all VOPs and stores them in thestoring medium 95, and edits a desired scene by combining them withother object videos provided through the Internet or a CD-ROM orDVD-ROM, the decoding apparatus with the configuration of the presentembodiment can make a high speed access to a picture at a desired timein the video pictures acquired, thereby enabling the video editionwithout stress. Furthermore, the video contents can be stored in a largecapacity recording medium such as a DVD-RAM with their VOPs being intracoded by the compression standard according to the MPEG-4, so thatdesired edition can be achieved with making high speed access to producea television program.

Although the present embodiment 7 is described by way of example ofdecoding the coded bit stream 39 including in the VOL header the objectintra-coded indicator signal 7′, display time multiplex identificationinformation 34 and time codes 35 as shown in FIG. 15, the presentinvention is not limited to this. For example, the same concept isapplicable to the VOP decoder for decoding the coded bit stream 40 or 41as shown in FIG. 16 or 17.

For example, because the VOP time code contained in the GOV ismultiplexed for each GOV, it is enough for the VOP decoder for decodingthe coded bit stream 40 as shown in FIG. 16 to be configured such thatthe VOL header analyzer 106 decodes only the object intra-codedindicator signal 7′, and the GOV header analyzer 61 decodes the displaytime multiplex identification information 34 and time codes 35 inresponse to the object intra-coded indicator signal 7′. In this case, asfor the GOV including the display time multiplex identificationinformation 34 which is ON, the high speed random access can beimplemented for all the VOPs in the GOV.

As for the VOP decoder for decoding the coded bit stream 40 as shown inFIG. 17, it can be configured such that the GOV header analyzer 61decodes the object intra-coded indicator signal 7′, display timemultiplex identification information 34 and time codes 35, so that therandom access function can be defined for each GOV independently.

Although the foregoing embodiments 1-7 describe the image codingapparatus or image decoding apparatus according to the MPEG-4 thatdefines the coded (decoded) images in the form of the object-based VOPs,and codes the images on an object by object basis, the present inventionis not limited to this. For example, it is applicable to the imagecoding apparatus, image coding method, image decoding apparatus andimage decoding method according to the MPEG-1 or MPEG-2 that does nothave the concept of the object or VOP. In this case, coded images atrespective times or image frames in a television signal, whichconstitute a moving picture sequence, correspond to the VOPs in theforegoing embodiments 1-5. Thus, replacing the VOPs by the coded imagesor image frames makes it possible to handle them in the same manner asin the embodiments 1-7.

For example, the MPEG-1 or MPEG-2 reserves a user data area which allowsa user to define data freely, or bit fields for future functionalextension. Thus, defining the syntax according to the present inventionin these data areas can improve the function of the random access orframe skip control.

Although in the foregoing embodiments 1-7, the object intra-codedindicator signal 7′ is described as the information indicating whetherall the VOPs included in the VOL- or GOV-based moving picture sequenceaccording to the MPEG-4 are intra coded or not, the present invention isnot limited to the VOL- or GOV-based moving picture sequence. Forexample, as for the VOPs that constitute any units of the moving picturesequence, or defines the moving picture sequence, the object intra-codedindicator signal 7′ can serve as information indicating whether all theVOPs included in the moving picture sequence based on the units otherthan the VOL or GOV are intra coded or not. This holds true when theVOPs are replaced by the coded images or image picture frames.

INDUSTRIAL APPLICABILITY

As described above, the image coding apparatus and image coding methodare based on the MPEG-4, and are suitable for coding images on an objectby object basis.

Furthermore, the image decoding apparatus and image decoding methodaccording to the present invention are also based on the MPEG-4, and aresuitable for decoding the coded bit stream in which the images are codedon the object by object basis.

1. An image encoding method to encode a moving picture sequence as acoded bit stream, comprising: utilizing a multiplexer to multiplexheader information into the coded stream, wherein the header informationincludes a singular intra-code indicator operable to notify a decoderwhen a plurality of frames in the moving picture sequence are allintra-coded before the decoder starts to decode the plurality of frames;and encoding macroblocks of a frame as intra-coded macroblocks when theintra-code indicator signals that the plurality of frames in the movingpicture sequence are intra-coded.
 2. An image encoding apparatus toencode a moving picture sequence as a coded bit stream, comprising: amultiplexer for multiplexing header information into the coded stream,wherein the header information includes a singular intra-code indicatoroperable to notify a decoder when a plurality of frames in the movingpicture sequence are all intra-coded before the decoder starts to decodethe plurality of frames, and the apparatus encodes macroblocks of aframe as intra-coded macroblocks when the intra-code indicator signalsthat the plurality of frames in the moving picture sequence areintra-coded.